A Russian airstrike targeting the Ukrainian city of Mariupol killed 300 people last week, including women, children and the elderly, according to Ukrainian authorities. Officials said the strike is the deadliest attack on Ukrainian civilians since the conflict began more than a month ago.

A statement posted by the Mariupol City Council on Telegram explained that the word Russian word for “CHILDREN” had been displayed in giant lettering on the ground outside the Drama Theater of Mariupol in an attempt to deter Russian forces from attacking the building that was being used as a civilian shelter.

“The occupier knew where he was hitting. He knew what the consequences might be, and anyway the bombs fell on the place, which became a refuge for hundreds of Mariupol residents,” the statement said, according to Google Translate. “There cannot be and never will be an explanation for this inhuman cruelty. As never will there be forgiveness for those who brought devastation, pain and suffering to our home.”

President Joe Biden’s national security adviser, Jake Sullivan, said the attack demonstrated “a brazen disregard for the lives of innocent people.”

Sullivan added that the reaction to the strike was “just absolute shock, particularly given the fact that it was so clearly a civilian target.”