The United Nations Security Council on Monday will hold a meeting to discuss the deteriorating humanitarian situation in Ukraine after more than 1.7 million Ukrainians have so far crossed into central Europe.
The meeting was expected to start at 2000GMT, three diplomats said.
The United Nations has been at the forefront of diplomatic efforts urging an end to Russia's invasion of Ukraine.
Russia has called the campaign it launched on February 24 a "special military operation".
France and Mexico last week worked on a resolution to the UN Security Council to address the humanitarian impact, but it was unclear if it would be formally tabled on Monday's meeting.
A total of 1,735,068 civilians - mostly women and children, as men stayed home to fight - have crossed the border into central Europe, the UNHCR said.
Poland, which has the largest Ukrainian community in the region - has received more than 1 million Ukrainian refugees, with the milestone passed late on Sunday.