Russian forces shelled Ukraine’s second-largest city on Monday, rocking a residential neighbourhood, and closed in on the capital, Kyiv, in a 17-mile convoy of hundreds of tanks and other vehicles, as talks aimed at stopping the fighting yielded only an agreement to keep talking.

The country’s embattled president said the stepped-up shelling was aimed at forcing him into concessions.

“I believe Russia is trying to put pressure (on Ukraine) with this simple method,” Ukrainian President Volodymyr Zelenskyy said late Monday in a video address. He did not offer details of the hourslong talks that took place earlier, but said that Kyiv was not prepared to make concessions “when one side is hitting each other with rocket artillery.”

Amid ever-growing international condemnation, Russia found itself increasingly isolated five days into its invasion, while also facing unexpectedly fierce resistance on the ground in Ukraine and economic havoc at home.

For the second day in a row, the Kremlin raised the spectre of nuclear war, announcing that its nuclear-capable intercontinental ballistic missiles, submarines and long-range bombers had all been put on high alert, following President Vladimir Putin’s orders over the weekend.

Stepping up his rhetoric, Putin denounced the U.S. and its allies as an “empire of lies.”