LVIV, Ukraine (Reuters) - Ukraine described the situation in Mariupol on Monday as "very difficult" and said it had been unable to establish a new safe corridor to evacuate civilians from the besieged city after it defied a Russian ultimatum to surrender.

       Russia's military had ordered Ukrainians inside the southeastern city to surrender by 5 a.m. (0300 GMT), saying that those who did so would be permitted to leave through safe corridors.

       "Of course we rejected these proposals," Deputy Prime Minister Iryna Vereshchuk said.

       Mariupol, a port on the Azov Sea, was home to 400,000 people before the war. It has been under siege and bombardment, with no food, medicine, power or fresh water, since the early days of Russia's invasion on Feb. 24.

       Vereshchuk said agreement had been reached with Russia on creating eight humanitarian corridors to evacuate civilians from besieged towns and cities on Monday but Mariupol was not among them. Russia denies targeting civilians.

       Vereshchuk said efforts to reach Mariupol with humanitarian supplies continued to fail.

       "The situation there is very difficult," she added.

       (Reporting By Natalia Zinets, Editing by Timothy Heritage)