Ukraine on Tuesday announced the establishment of seven escape corridors for the evacuation of civilians.
However, residents of the besieged port city of Mariupol would only be able to leave in private cars, Ukrainian Deputy Prime Minister Iryna Vereshchuk said, according to the Ukrinform news agency.
She accused Russian troops of continuing to block aid convoys from reaching Mariupol.
Kiev and Moscow have been accusing each other of sabotaging the escape of civilians for weeks.
According to Vereshchuk, Red Cross workers who were reportedly detained in the village of Manhush, about 20 kilometres west of Mariupol, have since been released.
On Tuesday, the Red Cross was to start a new attempt to bring people there in buses to the city of Zaporizhzhya.
About 600 Russian soldiers are currently being held as prisoners of war by Ukraine, according to Vereshchuk.
They are looking for ways to reach Ukrainians in Russian war captivity through the Red Cross and want to get Russia to release them, she said.
In the areas of the self-proclaimed Donetsk and Luhansk People’s Republics, some people have been Russian prisoners of war since 2014.