Ukraine's President Volodymyr Zelenskyy said late Tuesday he sees "positive" signals from Ukraine-Russia peace talks held in Istanbul, but vowed that Kyiv will not "decrease our defense efforts."

"We can say that the signals that we hear from the negotiations are positive, but those signals do not drown out the explosions or Russian shells," Zelenskyy said in a video address.

Zelenskyy also expressed skepticism about Moscow's stated plan of a military scaleback, saying: "We will not decrease our defense efforts."

There can be no talk of lifting sanctions imposed on Russia over its invasion of Ukraine until the war ends, he added.

"The question of sanctions cannot even be raised until this war is over, until we get back what is ours."

Russia pledged to scale down fighting around two Ukrainian cities including Kyiv following peace talks on Tuesday, but the United States led a chorus of sharp skepticism over Moscow's intentions.

The talks between Russia and Ukraine in Istanbul raised hopes after more than a month of war that has left thousands dead, and prompted negotiators to suggest a meeting between the two presidents.

On the ground, the violence was still having a devastating impact, as Ukraine said at least nine people were killed and 28 wounded Tuesday by a Russian airstrike on a government building in the southern city of Mykolaiv.

Following the talks in Turkey though, Ukrainian negotiator David Arakhamia said there were "sufficient" conditions for Zelenskyy and his Russian counterpart Vladimir Putin to meet in a bid to end Europe's worst conflict in decades.

Russian Deputy Defense Minister Alexander Fomin said there had been progress in talks on "the neutrality and non-nuclear status of Ukraine."

"A decision has been made to radically, by several times reduce the military activity" around the capital Kyiv and the city of Chernihiv, he said.

Russia's chief negotiator Vladimir Medinsky said there had been a "meaningful discussion" at the talks.

But the United States immediately cast doubt on Moscow's words, and Western leaders vowed to keep "raising the costs" on Russia for its invasion.

U.S. officials said that while a small number of Russian forces were stepping back from Kyiv, the vast majority of its positions remained.

"We're not prepared to call this a retreat or even a withdrawal," Pentagon spokesperson John Kirby said.

"We all should be prepared to watch for a major offensive against other areas of Ukraine... It does not mean that the threat to Kyiv is over."

A spokesperson for British Prime Minister Boris Johnson joined in the distrust, saying: "We will judge Putin and his regime by his actions and not by his words."

U.S. President Joe Biden meanwhile spoke with Johnson and the leaders of France, Germany and Italy as they sought to harden their unified stance against Moscow.

"The leaders affirmed their determination to continue raising costs on Russia for its brutal attacks in Ukraine as well as to continue supplying Ukraine with security assistance," the White House said in a readout of the call.

Following Tuesday's announcements, European and U.S. stock markets lifted and oil prices fell by 5% as supply fears eased, while the ruble surged 10% against the dollar.

In response to the invasion, the West has imposed crushing economic sanctions and many companies have exited Russia.

There have also been several rounds of diplomatic expulsions, which continued Tuesday with Belgium, Ireland and the Netherlands announcing a total of 42 diplomats would be expelled.