At the meeting, the UN's 193 member states will take a position on a resolution that is now being prepared on the annexation, after Russia last week vetoed a condemnation in the Security Council, diplomatic sources said.
According to UN spokeswoman Paulina Kubiak, the issue is being raised at the request of Ukraine and Albania.
Russia annexed the four regions on Friday, in violation of international law.
The announcement has been met with strong condemnations worldwide.