MAIN HEADLINES

• Ukrainian President Volodymyr Zelenskyy says he is ready for talks with Russian leader Vladimir Putin, saying a meeting "in any format" was needed to end the war.

• U.S. President Joe Biden has warned Russia it would pay a "severe price" if it uses chemical or biological weapons in Ukraine, claiming there was a "clear sign" Moscow was planning to do so.

• Russia is boosting its air and sea military operations in Ukraine, according to the Pentagon, which says Moscow has flown more than 300 missions in the past 24 hours in a move to break Ukrainian resistance.

• Russian artillery continues to blast the eastern cities of Kharkiv, Sumy and Chernihiv but Ukraine's military has claimed Russian ammunition and food stocks will last for "no more than three days."

• A Ukrainian MP for Odesa has said he anticipates a Russian land operation against the city launched from the Black Sea as residential areas in the city were reportedly targeted for the first time on Monday.

• However, the strategic southern city of Mariupol, devastated by Russian shelling, remains the focus of intense fighting, with reports of those still trapped in the city experiencing extreme hunger and dehydration. 

• Ukraine says a further 8,000 people were evacuated from conflict zones on Monday, including around 3,000 people from Mariupol.

• Kyiv mayor Vitali Klitschko has announced a new curfew for the capital from 8:00 pm (1800 GMT) on Monday to 7:00 am on Wednesday. 

• A ninety-six-year-old Holocaust survivor has been killed by Russian shelling in Kharkiv, with Zelenskyy honoring the victim in a public address: "Please think about how many things he has come through."

• Kyiv has accused Russian forces of firing on unarmed protesters in the occupied southern city of Kherson after videos emerged allegedly showing residents fleeing bursts of gunfire during a protest against Russia's actions.

• A Russian court has branded Facebook and Instagram as "extremist" and banned them as part of a wider Kremlin crackdown on sharing information on the Ukraine conflict. 

• Russia warned the U.S. ambassador to Moscow relations are "on the verge of rupture" after Biden called Putin a "war criminal." 

• The EU cannot agree on whether or how to impose sanctions on Russia's energy sector, with Germany and the Netherlands saying the single market is currently too dependent on Russian oil and gas to impose an embargo now. 

• Nobel peace prize-winner and the editor of Russian news outlet Novaya Gazeta, Dmitry Muratov, is to put his gold medal up for auction to raise money for Ukrainian refugees.

• The World Health Organization says it has verified 62 separate attacks on healthcare facilities in Ukraine since the conflict started.

• Nearly 3.5 million Ukrainians have now fled the country, the UN says, with 10 million displaced from their homes.

IN DETAIL

Chemical weapons claims

U.S. President Joe Biden on Monday issued his strongest warning yet that Russia is considering using chemical weapons, saying there were "a clear sign" Moscow intended to use both.

Russia has said in recent weeks that Ukraine might possess chemical or biological weapons, accusations Biden said were not only false, but an indicator that Moscow could be planning to use such weapons itself.

"Now he's talking about new false flags he's setting up including, asserting that we in America have biological as well as chemical weapons in Europe, simply not true," Biden said at a business event.

"They are also suggesting that Ukraine has biological and chemical weapons in Ukraine," he added. "That's a clear sign he's considering using both of those."

As Russia intensifies its bombardment of Ukrainian cities, Washington has intensified its rhetoric against Moscow, with Biden going so far as to describe Russian President Vladimir Putin as a "war criminal".

Accusations of war crimes

Russia's foreign ministry summoned the U.S. ambassador to tell him that Biden's accusations had put Moscow-Washington relations "on the verge of rupture." 

The ministry also told Ambassador John Sullivan that hostile actions against Russia would receive a "decisive and firm response."

Biden last week accused the Russian leader of war crimes in Ukraine for targeting civilians, which is considered a breach of the Geneva Conventions, agreements that specify international humanitarian laws to be followed in war time. 

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The International Criminal Court's chief prosecutor, Karim Khan, opened an investigation into possible war crimes in Ukraine. However, a prosecution of Russia's leaders would be difficult and could potentially take years.

Legal experts said the bombings in Mariupol of a maternity hospital and a theater marked as sheltering children could fall under the definition of war crimes, but prosecutors would have to prove intent and link leaders directly to specific attacks.

Neither Russia nor Ukraine is a member of the ICC and Moscow does not recognize the tribunal. The Kremlin earlier described the claims against Putin as a "personal insult."

Peace talks

Despite the war of words, Ukrainian President Volodymyr Zelenskyy said on Monday that it would only be possible to negotiate an end to the conflict by meeting Putin.

"I believe that until such time as we have a meeting with the president of the Russian Federation...you cannot truly understand what they are prepared to do in order to stop the war and what they are prepared to do if we are not ready for this or that compromise," he said.

Zelenskyy has sought a meeting with the Russian leader for nearly a year, but Putin has refused, saying the Ukrainian president should resolve his country's "civil war" with separatist territories linked to Moscow.

Last week Zelenskyy called for a meeting so that Russia could "limit the losses caused by its mistakes." On Monday he repeated that Ukraine could not now secure NATO membership.

NATO member states, he said, "understand that they do not want to fight with Russia and therefore cannot take us in...we have to reconcile ourselves to that and say 'ok, other guarantees'."

However, he added several conditions would need to be met before such matters could be dealt with, including a ceasefire, the withdrawal of troops and security guarantees.

"If people are trying to stop a war, there is a cease-fire and troops are withdrawn. The presidents meet, reach an agreement on withdrawing troops and there are security guarantees of one sort or another," he said. 

"Compromises must be found, one way or another of guaranteeing our security," he added.

Russian spokesperson Dmitry Peskov said on Tuesday Russia did not intend to make public its detailed demands to Ukraine, but it would like the negotiations with Kyiv to be more "active and substantive".