SEOUL, South Korea (AP) — North Korean officials offered a rare public apology for the collapse of an apartment building under construction in Pyongyang, which a South Korean official said was believed to have caused considerable casualties that could mean hundreds might have died.

The word of the collapse in the secretive nation’s capital was reported Sunday morning by the North’s official Korean Central News Agency, which gave no death toll but said that the accident was “serious” and upset North Korea’s leader, Kim Jong Un.