KYIV - Russian planes bombed an institute in the Ukrainian city of Kharkiv that is home to an experimental nuclear reactor and a neighbouring hostel is on fire, a senior Ukrainian official said on Thursday (March 10).

Mr Anton Gerashchenko, an adviser to the minister of internal affairs, said in an online post that the Institute of Physics and Technology contained "sources of radiation used for scientific purposes".

The Interfax Ukraine news agency said the fire service was extinguishing a blaze in a five-story hostel which covered a total of 100 sqm.

The Ukrainian Parliament's official website had earlier said fighting close to the institute was continuing.

Russian forces last week captured the nuclear power station at Zaporizhzhia after an attack during which an adjacent training facility was set on fire.

Hundreds of thousands of civilians remained trapped in Ukrainian cities on Thursday, sheltering from Russian air raids and shelling as talks between Ukraine and Russia's foreign ministers made little apparent progress.

With Russian President Vladimir Putin's war in Ukraine entering its third week, officials in Mariupol said Russian warplanes again bombed the southern port city where a maternity hospital was pulverised on Wednesday.

The invasion has so far failed to reach its stated objectives. It has caused thousands of deaths and forced more than 2 million people to flee Ukraine, where several cities are under siege.

It has also hit the world's economy, still emerging from the effects of the coronavirus pandemic.

International Monetary Fund Managing Director Kristalina Georgieva said the war and the massive sanctions leveraged against Russia as punishment have triggered a contraction in global trade and sent food and energy prices sharply higher, which will force the IMF to lower its global growth forecast next month.

She said she expected mounting pressure on Russia to end the war, given the spillover effects it is having on economies around the world.

Mr Putin, facing global condemnation and increasingly isolated, said Russia would emerge stronger after overcoming the difficulties caused by the sanctions.

He told a government meeting there had been no alternative to what Russia calls its special military operation in Ukraine.

"There are some questions, problems and difficulties but in the past we have overcome them and we will overcome them," he said.

Russian Foreign Minister Sergei Lavrov and Ukraine's Dmytro Kuleba met in Turkey in the highest-level talks since Putin ordered the invasion on Feb 24.

Mr Kuleba said afterwards Mr Lavrov had refused to promise to hold fire to allow for aid distribution and the evacuation along humanitarian corridors of civilians trapped in Mariupol and elsewhere.

Mr Lavrov showed no sign of making any concessions, saying the operation was going to plan and repeating Moscow's accusations that Ukraine posed a threat to Russia, which wants Kyiv to drop any aspirations of joining the Nato alliance.

A ceasefire was not meant to be on the agenda at Thursday's talks in Antalya, Mr Lavrov added.

While there was no apparent progress towards a ceasefire, analysts said the fact the ministers were even meeting left a window open for ending the war.

The road ahead for any negotiation would be difficult, but Moscow's slower-than-expected military progress and the stinging cost of sanctions had potentially opened an opportunity for a compromise, they said.

In Washington, Central Intelligence Agency director William Burns said Mr Putin did not appear to have a "sustainable" end-game in Ukraine and might soon try to find a way to end the fighting.

Others, however, cautioned that Putin could still seek to escalate.

"We have moved the dial for the process from zero to at least having the possibility for a discussion. But the indications of troop movements toward Kyiv may indicate that the worst may still be ahead of us," said Jonathan Eyal at the Royal United Services Institute in London.

Attempts to send aid and evacuation convoys have failed for six days.

Aid agencies say humanitarian help is most urgently needed in Mariupol, where residents are running out of food, water and power. Its capture would allow Russia to link up pro-Moscow enclaves in the east and Russian-annexed Crimea to the south.

Russian warplanes targeted convoy routes on Thursday, said Mr Petro Andrushenko, an adviser to Mariupol's mayor.

"Air strikes started from the early morning. Air strike after air strike. All the historic centre is under bombardment,"he told Reuters by phone.

"They want to absolutely delete our city, delete our people.

They want to stop any evacuation."

Mr Lavrov said the hospital struck on Wednesday had stopped treating patients and had been occupied by Ukrainian "radicals".

Russia's Defence Ministry later denied having bombed the hospital, accusing Ukraine of a "staged provocation" there.

White House spokesman Jen Psaki called the hospital attack "horrific" and "barbaric," and said Washington was reviewing Russia's actions for possible war crimes.

European Commission President Ursula von der Leyen also said the "inhumane, cruel and tragic" attack could constitute a war crime and should be investigated.

Mr Lavrov accused Western countries of inflaming the situation by arming Ukraine.

Asked if the conflict could lead to nuclear war, he said: "I don't want to believe, and I do not believe, that a nuclear war could start."