US President Joe Biden believes that Russia's Vladimir Putin's "back is against the wall" in Ukraine, increasing the chance he may use chemical or biological weapons.

The White House also warns that Russia may also resort to cyber-attacks against the US in response to increasingly damaging sanctions.

Ukrainian President Volodymyr Zelenskyy said his country's forces have slowed down the enemy advance. But Ukraine's military says Russia has increased its "aviation presence" in the country's airspace in the last 24 hours.

Mr Zelenskyy has again called for a meeting with Putin, saying it will not be possible to negotiate an end to te war unless they meet.