Desperate civilians fled besieged Ukrainian cities on Tuesday after Russia offered "humanitarian corridors," as the number of refugees leaving the country since Moscow's invasion passed 2 million.

Civilians boarded buses out of the north-eastern city of Sumy, where 21 people were killed in air strikes overnight, while others took an unofficial

Jailed Kremlin critic Alexei Navalny on Tuesday urged Russians to continue protesting against Moscow's invasion of Ukraine, days after thousands of protesters were arrested at anti-war rallies nationwide.

More than 13,500 Russians have been detained at demonstrations against the invasion of Ukraine since President Vladimir Putin ordered his army to

Ukraine on Tuesday accused Russia of violating a humanitarian corridor aimed at enabling civilians to leave the beleaguered southern port city of Mariupol.

"The enemy has launched an attack heading exactly at the humanitarian corridor," the defense ministry said on Facebook, adding the Russian army "did not let children, women and elderly people

Sitting at a windswept terrace of a tiny bar in Georgia's capital Tbilisi, Russian exile Roman Mikhailov said he had no choice but to leave his country "immediately" when Moscow invaded Ukraine.

The 25-year-old logistics manager said the attack on Ukraine, which shocked the world, was a point of no return for some Russians who oppose President