At least 19 countries, including the U.S., Canada, 15 members of the EU, Ukraine and Albania, have expelled Russian diplomats over the poisoning of a former Russian spy in Britain.

Sergei Skripal, a former Russian officer who sold secrets to Britain and moved there in a 2010 spy swap, remains in critical condition along with his daughter, Yulia, after they were found unconscious on a park bench in the sleepy English city of Salisbury on March 4. Britain says a military-grade nerve agent was used to poison them, and accused Moscow of perpetrating the attack. The U.S., France and Germany have agreed it's highly likely that's the case.

The U.K. has already expelled 23 Russian diplomats over the incident, accusing them of being undeclared intelligence agents, which led Russia to expel the same number of British diplomats. The European Union has already recalled its ambassador to Russia.

Moscow's Foreign Ministry on Monday condemned the mass expulsion of Russian diplomats from NATO and EU member states and reiterated Russia's denial that it had any involvement with a chemical weapon attack on British territory.

"This unfriendly act by this group of countries will not go without consequences. We will react," the Foreign Ministry said in a statement.

British Prime Minister Theresa May welcomed on Monday the action of other countries to expel Russian diplomats, saying it sent a strong signal to Moscow that it cannot flout international law.

"We welcome today's actions by our allies, which clearly demonstrate that we all stand shoulder to shoulder in sending the strongest signal to Russia that it cannot continue to flout international law," a statement from May's office said.

British Foreign Secretary Boris Johnson said the Western action against scores of Russian diplomats in the United States and Europe was the biggest such expulsion of Russian spies ever.

"Today's extraordinary international response by our allies stands in history as the largest collective expulsion of Russian intelligence officers ever and will help defend our shared security," Johnson said on Twitter.

"Russia cannot break international rules with impunity."

Here is a short list of measures by Britain and its allies, and Russian countermeasures:

Britain: Expelled 23 Russians alleged to have worked as spies under diplomatic cover. Promised to freeze any Russian state assets that "may be used to threaten the life or property of UK nationals or residents".

The U.S.: Expelling 60 Russians, including 12 intelligence officers from Russia's mission to U.N. headquarters in New York. Closing Russian consulate in Seattle.

Canada: Expelling four Russians alleged to have worked as spies or interfered in Canadian affairs under diplomatic cover. Denying three applications for Russian diplomatic staff.

Among EU members, France, Germany, Poland are expelling four diplomats each, Czechia and Lithuania are expelling three diplomats each, Denmark, Italy, the Netherlands and Spain are expelling two diplomats each and Croatia, Estonia, Finland, Latvia, Romania and Sweden are expelling one diplomat each.

Ukraine, a non-EU country, joined the 14 states and expelled 13 Russian diplomats. Albania followed suit to expel two Russian diplomats.

Russian response: Russia has expelled 23 British diplomats and closed the British consulate in St Petersburg and the British Council cultural body.

Moscow will expel at least 60 staff from U.S. diplomatic missions in Russia, RIA news agency quoted Russian senator Vladimir Dzhabarov as saying. RIA also quoted an unnamed Foreign Ministry source as saying: "The response will be symmetrical. We will work on it in the coming days and will respond to every country in turn."

Joint reaction targets Moscow

Along with expelling 60 Russian diplomats, the Trump administration on Monday ordered Russia's consulate in Seattle to close.

Senior Trump administration officials said all 60 Russians were spies working in the U.S. under diplomatic cover, including a dozen at Russia's mission to the United Nations. The officials said the administration was taking the action to send a message to Russia's leaders about the "unacceptably high" number of Russian intelligence operatives in the U.S.

The expelled Russians will have seven days to leave the U.S, said the officials. They weren't authorized to be identified by name and requested anonymity. They added that the Seattle consulate is a counter-intelligence concern because of its proximity to a U.S. Navy base.

Canada ordered the expulsion of four Russian diplomats and denied credentials for three others.

"We are taking these measures in solidarity with the United Kingdom," Foreign Minister Chrystia Freeland said.

"The nerve agent attack in Salisbury, on the soil of Canada's close partner and ally, is a despicable, heinous and reckless act, potentially endangering the lives of hundreds," she said.

The four diplomats serving at either Russia's embassy in Ottawa or its consulate in Montreal have been "identified as intelligence officers or individuals who have used their diplomatic status to undermine Canada's security or interfere in our democracy."

Applications by Russia to add three more diplomatic staff in this country were denied for similar reasons.

Freeland called the nerve agent attack "a clear threat to the rules-based international order" and a breach of conventions against chemical weapons use.

She added it was "part of a wider pattern of unacceptable behavior by Russia, including complicity with the Assad regime (in Syria), the annexation of Crimea, Russian-led fighting in eastern Ukraine, support for civil strife in Ukraine, Georgia, Moldova and other neighboring countries, interference in elections, and disinformation campaigns."

EU Council Donald Tusk announced Monday that more than a dozen European countries had expelled Russian diplomats, adding that there may be additional measures including further expulsions in the coming days and weeks.

Croatia will declare one Russian diplomat 'persona non grata' as a political message of solidarity with Britain, Prime Minister Andrej Plenkovic said on Monday.

"We thus show that we do not accept such an attack to which the United Kingdom has been exposed," Plenkovic said, without providing any details on the diplomat to be expelled.

Czechia said it is kicking out three staffers from the Russian embassy. Andrej Babis calls the measure an expression of solidarity with Britain.

Denmark, Finland and the Netherlands said Monday they had ordered the expulsion of Russian diplomats over the poisoning of a former spy and his daughter in England, as EU nations step up the pressure on Moscow.

Denmark, the only Nordic country to be both a member of NATO and the EU, said it was two diplomats.

"There is no doubt about our solidarity with Britain," Danish Foreign Minister Anders Samuelsen told reporters.

"We agree with Britain that it is very likely that Russia is behind (the nerve agent attack). There are no other plausible explanations," he said, urging Russia "to change course."

He did not disclose the identities nor the functions of the two diplomats to be expelled, but said they had one week to leave the country.

Estonia said it would expel Russia's defense attache in the country, saying that his actions are not compatible with the Vienna Convention.

"This afternoon we called in the Russian ambassador to whom we gave a note that the defense attache at the Russian Embassy should leave the country," Foreign Minister Sven Mikser told a news conference.

Russia's northwestern neighbor Finland said Monday it was to expel one Russian diplomat.

"The expulsion will be put into effect simultaneously with the corresponding actions of other EU member states," the Finnish government statement said.

The announcement was made after a meeting between President Sauli Niinisto and the ministerial committee on Foreign and Security Policy that is chaired by Prime Minister Juha Sipila.

Germany on Friday announced its decision to expel four Russian diplomats, with Foreign Minister Heiko Maas announcing Berlin's decision on Twitter.

"Today we have expelled four Russian diplomats from Germany," he said. "This is a signal of solidarity with Great Britain."

Maas slammed Moscow for not cooperating with Britain in the investigation into the poisoning of ex-Russian spy Skripal and his daughter Yulia.

"Since the poisoning attack in Salisbury, Russia has still not contributed to shed light on the incident," he said.

The Italian foreign ministry said in a statement that two Russian diplomats must leave Italy within a week.

"As a sign of solidarity with Great Britain and in coordination with NATO allies and European partners, the foreign ministry today communicated its decision to expel from Italian territory within a week two officials at the Russian embassy in Rome who have diplomatic credentials," the statement said.

Latvia said on Monday it would expel one Russian diplomat out of solidarity with Britain.

"In solidarity with U.K. over #SalisburyAttack and for violation of Vienna convention Latvia joins many #EU countries expelling Russian diplomats as well as blacklisting a Russian citizen," Edgars Rinkevics, Latvia's foreign minister, said on Twitter.

Lithuania's Ministry of Foreign Affairs said it would expel three Russian diplomats and would also ban a further 44 people from entering the country.

"By expelling persons who engaged in activities incompatible with their diplomatic status, the countries are expressing their solidarity with the United Kingdom and seeking to take action against Russia's spy networks in Europe," the ministry said in a statement.

The Netherlands said it was expelling two diplomats. Dutch Prime Minister Mark Rutte said on Twitter the Russian envoys had "two weeks to leave the Netherlands."

Polish Foreign Minister Jacek Czaputowicz told a news conference that the four Russian diplomats were to leave the country by April 3.

"Showing solidarity with Britain and other countries is the most important thing," Czaputowicz said. "There are diplomatic costs to that but they are worth it."

Romania will expel one Russian diplomat over the nerve agent attack, the foreign ministry said on Monday.

"In solidarity with Britain and in accordance with provisions of the Vienna Convention ... the foreign affairs ministry has notified the Embassy of the Russian Federation in Bucharest that a diplomat will be declared persona non grata and is obliged to leave Romanian territory."

Austria, however, said it would not follow suit in expelling Russian diplomats, stressing its neutrality.

"We stand behind the decision to recall the EU ambassador, but we will not take any national measures," Chancellor Sebastian Kurz and Foreign Minister Karin Kneissl said in a joint statement.

"Indeed, we want to keep the channels of communication to Russia open," they added. "Austria is a neutral country and sees itself as a bridge-builder between East and West."

Ukrainian President Petro Poroshenko says his nation is expelling 13 Russian diplomats, acting in sync with the U.S. and the EU nations.

Poroshenko says on Facebook that Ukraine is acting in the "spirit of solidarity" with its "British partners and trans-Atlantic allies." The U.S. is kicking out 60 Russian diplomats, Germany and Poland said they have asked four Russian diplomats to leave and other EU nations have made similar moves.

Russia and Ukraine have been in a tug-of-war since Moscow's 2014 annexation of Ukraine's Crimean Peninsula and support for pro-Russia separatists in eastern Ukraine.

Poroshenko on Monday called for further "raising the price" for Moscow through financial and economic sanctions.