Seven key developments in the Ukraine conflict this weekend By

(CNN)Civilian casualties continue to mount as a result of Russian attacks on Ukraine, and the besieged city of Mariupol has refused to surrender despite constant bombardment. Here are the key developments from the weekend.

Ukrainian officials reject Russian request to surrender Mariupol
Russian forces continued their assault on the southeastern city of Mariupol, striking an art school turned bomb shelter on Sunday.
The city council put the number sheltering in the school building at 400, but Petro Andrushenko, an adviser to the city mayor, said it was not clear how many people were there.
A satellite image from March 20 shows the extent of destruction in Mariupol.
A satellite image from March 20 shows the extent of destruction in Mariupol.
In a video message late Sunday, Ukrainian President Volodymyr Zelensky said there were no military positions near the art school.
Most of the people sheltering there were "women and children, the elderly. They are under the rubble. We do not know how many are alive now, but we know that the pilot who dropped that bomb will definitely be shot down," he said.