Russian President Vladimir Putin laid out conditions late on February 28 for ending his military offensive in Ukraine, as Moscow's forces shelled the country's second city and Western nations prepared even more sanctions.

Putin's ultimatum came as Moscow and Kyiv held their first talks since the outbreak of war on February 24, which shocked the world and provoked a massive diplomatic, economic, cultural and sporting backlash.

Shortly before the talks broke up, agreeing merely to hold a second round of negotiations "soon", Putin laid out his prerequisites for ending the war in a phone call with French President Emmanuel Macron.

"Putin stressed that a settlement is possible only if Russia's legitimate security interests are unconditionally taken into account, including the recognition of Russian sovereignty over Crimea, the demilitarisation and denazification of the Ukrainian state and ensuring its neutral status," the Kremlin said.

Fighting continued to rage during the dialogue, with at least 11 people killed by Russian attacks in Ukraine's second-largest city of Kharkiv, near the Russian border.

More than 350 civilians, including 14 children, have been killed during the invasion, Ukraine said, while more than half a million people have fled the country.

Oleg Sinegubov, the governor of the region that includes Kharkiv, said the "Russian enemy is bombing residential areas of Kharkiv, where there is no critical infrastructure, where there are no positions of the armed forces".

An AFP photographer in the city inspected damage caused by fighting on February 27, finding a destroyed school, as well as several burned out Russian infantry vehicles.

Russian corpses in army fatigues could also be seen in the streets.

In Kyiv, many were preparing for a fresh assault with makeshift barricades dotting the streets.

The Russian army urged Ukrainians to leave Kyiv "freely" on one highway out ahead of what is an expected Russian offensive to capture the capital.

The International Atomic Energy Agency said it was "gravely concerned" as Russian forces advanced towards Ukraine's largest nuclear plant, strongly warning against any military action that could threaten the Zaporizhzhia facility.