KYIV (Reuters) -Ukraine hopes on Friday to evacuate civilians who are holed up in a vast steel works with the last fighters defending the southern city of Mariupol.

       "An operation is planned today to get civilians out of the plant," President Volodymyr Zelenskiy's office said without giving details.

       U.N. Secretary-General Antonio Guterres said after meeting Zelenskiy in Kyiv on Thursday that intense discussions were under way to enable the evacuation of the Azovstal steel plant, which has been pounded by Russian forces occupying Mariupol.

       On Tuesday, Russian President Vladimir Putin agreed "in principle" to U.N. and International Committee for the Red Cross involvement in evacuating the Azovstal plant.

       The Mariupol city council has said about 100,000 residents across the city are "in mortal danger" because of Russian shelling and unsanitary conditions, and described a "catastrophic" shortage of drinking water and food.

       (Reporting by Natalia Zinets, Editing by Timothy Heritage)