The Kremlin on Friday accused the U.S. authorities of acting in an unacceptable way by not issuing entry visas to a Russian military delegation which had been due to attend a briefing at the United Nations headquarters in New York.

A group of senior officers from the general staff of the Russian armed forces could not attend the joint briefing on Thursday with the Chinese military at the U.N. because they had no U.S. visas, said Alexander Emelianov, from the Russian Defense Ministry international cooperation committee.

"As a country hosting the United Nations headquarters and its structures, the U.S. authorities bear certain obligations. Certainly, in this case we are very worried by such a situation and consider it unacceptable," Kremlin spokesman Dmitry Peskov told a regular conference call with reporters.

Moscow had previously accused the United States of searching its missions and diplomatic staff's accommodation. Washington ordered the shutdown of the Russian diplomatic missions in a retaliatory move after the Kremlin demanded the U.S. slash staff numbers at its missions in Russia.

The latest diplomatic spat is the latest twist in tortured ties between the US and Russia, which have slumped to their lowest point since the Cold War following the Kremlin's seizure of Crimea from Ukraine in 2014. The West slapped punishing sanctions on Russia over its meddling in its ex-Soviet neighbor, sparking a revenge embargo from Moscow against agricultural products.

Moscow lodged a protest with Washington, accusing U.S. officials of tearing down Russian flags from two of its diplomatic missions in the country, the foreign ministry said on Thursday.

Russian news agencies cited the Russian embassy as saying it had lodged a formal protest over the incident. "A strong protest was sent to the American side in relation to Russian flags being torn down at our diplomatic properties in San Francisco, which are under the control of U.S. authorities," Interfax news agency quoted the embassy as saying in a statement. "We consider this as an extremely unfriendly step," the embassy said.

In late August, the United States ordered Russia to close its consulate in San Francisco and two other installations as relations between the two former Cold War enemies took another dive.

Earlier Russia's envoy to Washington Anatoly Antonov said he had sent a "decisive protest" to the U.S. over the removed flags. "Such steps only complicate US-Russian dialogue," he said in televised remarks.

"We demand an immediate end to the takeover of our property in the US which is accompanied by offensive actions," Antonov added.

"The flags at the former Russian consular properties in San Francisco were respectfully lowered and are safely stored within each of the buildings," a U.S. State Department official said in an email.