‘Russia could use chemical or biological weapons in Ukraine’

Western officials - including the White House - have warned Russia could use chemical or biological weapons in Ukraine or create a “false flag” operation - a misleading operation blamed on the other side, usually used to justify a supposed counter-attack.

At his press conference Mr Lavrov repeated Russia’s claim that the Pentagon was using Ukrainian territory to develop pathogens that could be used to create biological weapons - an assertion the US has called “preposterous”.

He also alleged that Ukraine had been preparing an attack against two Russia-backed separatist regions in eastern Ukraine.

Moscow earlier said Ukrainian forces had transported some 80 tonnes of ammonia in the country’s north-east, without providing evidence.

The US House of Representatives voted in favour of nearly $14bn (£10.6bn) in aid for Ukraine, as well as voting to ban US imports of Russian oil and other energy products. The measures still must pass through the Senate, which is expected to vote later this week.

Meanwhile US Vice-President Kamala Harris is in Poland, a day after Washington rejected the country’s plan to transfer military jets to the US, rather than directly to Ukraine.

And in Europe, EU leaders are meeting in France’s Palace of Versailles for a two-day summit to discuss Ukraine’s possible future membership, more sanctions on Russia, and a new common defence policy.

US officials estimated that between 5,000 to 6,000 Russian troops have been killed in Ukraine since the war began on 24 February.

Ukraine says more than 12,000 Russian service personnel have died, while Russia last week acknowledged 498 fatalities - but none of the competing claims can be clearly verified.