Russian troops are making an all-out attempt to seize control of eastern Ukraine, and their message is simple: Surrender or die.

Many locals are fleeing, but the prospect of more brutal shelling raises concern for those who can only take cover and hope.

Ukraine's Azov Battalion released new footage purportedly showing civilians sheltering in a steel plant in the heavily bombarded port city of Mariupol. The local council says they number more than 1,000.

A woman in the video says, "I evacuated with my three children. The conditions here are hard for them. They can't study and there is?little to eat."

On Tuesday, a spokesperson for a pro-Russian separatist militia said specially selected assault groups had launched an attack on the plant.

More details are emerging about a Russian cruiser that sank in the Black Sea last week. Independent media in Europe and Russia say dozens of crew members died on the Moskva, raising doubts about Moscow's claim that all survived.