President Vladimir Putin introduced martial law on Wednesday in four Ukrainian regions he says are part of Russia as some residents of the Russian-held city of Kherson left by boat after Moscow warned of a looming assault.

The images of people fleeing Kherson were broadcast by Russian state TV, which portrayed the exodus — from the right bank of the Rover Dnipro to its left bank — as an attempt to clear the city of civilians before it became a combat zone.

Kirill Stremousov, deputy head of the local Russia-backed administration, made a video appeal after Russian forces in the area were driven back by 20 to 30 kilometers in the last few weeks. They risk being pinned against the western bank of the 2,200-km-long Dnipro river that bisects Ukraine.