Ukraine hopes to evacuate women, children and elderly from Mariupol on Wednesday

"We managed to pre-agree a humanitarian corridor for women, children and older people," she wrote on Facebook. "Given the catastrophic humanitarian situation in Mariupol, this is where we will focus our efforts today."

Local authorities say thousands of people have been killed in the siege of Mariupol and that the port city on the Sea of Azov has been all but destroyed.

A previous agreement to create a humanitarian corridor for civilians to leave Mariupol collapsed on March 5. Since then, repeated efforts to create a safe corridor have failed, with each side blaming the other.

Vereshchuk said the attempted evacuation would start at 2 p.m. (1100 GMT).

"Given the very difficult security situation, changes may occur during the corridor action. So, please follow the relevant official messages," she said.

Russia launched a large-scale invasion of Ukraine on Feb. 24. Moscow has given the last Ukrainian defenders at a steel works in Mariupol an ultimatum to surrender.

Moscow denies targeting civilians in what it calls a "special military operation" in Ukraine, which it says is aimed at demilitarizing Ukraine and rooting out dangerous nationalists. Kyiv and the West dismiss Russia's stance as an unjustified pretext for an invasion.