Ukrainian President Volodymyr Zelenskyy on Tuesday said the signals from peace talks with Russia could be called positive but added that they did not drown out the explosions from Russian shells.

In a late-night address, Zelenskyy also expressed caution about Russia's promise to sharply curtail military action in some areas and said Ukraine would not be easing off its defensive efforts.

Russia and Ukraine have been holding peace negotiations in an Istanbul palace. Zelenskyy said Kyiv saw no reason to believe in words from some Russian representatives.

"We can say the signals we are receiving from the talks are positive but they do not drown out the explosions of Russian shells," he said, adding that Ukraine could only trust a concrete result from the talks.

Earlier in the day, Russia promised to scale down military operations around Ukraine's capital and north.

Zelenskyy said that despite this vow, "the situation has not become easier ... the Russian army still has significant potential to continue attacks against our state." He added: "Therefore we are not reducing our defensive efforts."

Zelenskyy reiterated that for any peace deal to work, Russian troops would have to leave and there could be no compromise on Ukraine's sovereignty and territorial integrity.

He also called for tougher sanctions against Russia and ruled out the idea of current punitive measures being lifted until the war was over and justice had been restored. 

Earlier on Tuesday, U.S. President Joe Biden expressed his own feelings on Russia's announced plans, maintaining a degree of skepticism in remarks at the White House.

“We’ll see," Biden said. "I don’t read anything into it until I see what their actions are.”

Indeed, U.S. and Western officials have expressed skepticism about Russia's announcement earlier on Tuesday that it would dial back operations in an effort to increase trust in ongoing talks between Ukrainian and Russian officials in Turkey.

The Associated Press contributed to this report.