Russia has increasingly focused its strikes on the capital Kyiv. Kyiv has been targeted in 17 out of 21 reported Russian attacks on Ukraine in May, compared with twice out of seven attacks in April.

"Let me remind you, there's Alaska across the strait," Russia State Duma Deputy, Andrey Gurulyov said on state-run TV.

The wall of a major dam in a part of southern Ukraine that Moscow controls collapsed Tuesday after a reported explosion, sending water gushing downriver and prompting dire warnings of ecological disaster as both sides in the war ordered residents to evacuate.

Hundreds of thousands of Ukrainian residents have been evacuated from their homes over concerns of flooding due to damage sustained to a Ukrainian dam.

A torrent of water burst through a huge dam on the Dnipro River that separates Russian and Ukrainian forces in southern Ukraine on Tuesday, flooding a swathe of the war zone and forcing villagers to flee.

Ukraine and Russia accused each other on Tuesday of blowing up a dam and causing widespread flooding in southern Ukraine, while Russia said it had thwarted another Ukrainian offensive in eastern Donetsk and inflicted heavy losses.