Look for things to heat up in Afghanistan.

KABUL (Reuters) - At least seven children were killed in a U.S.-led coalition air strike on a religious school in Afghanistan, the coalition said on Monday, amid rising anger over civilian deaths from foreign military operations.

A U.S. military spokesman said some children who survived Sunday’s raid said insurgents had forced pupils to stay inside the madrasa.

“We are truly sorry for the innocent lives lost in this attack,” said Army Major Chris Belcher, a coalition spokesman, in a statement. “We had surveillance on the compound all day and saw no indications there were children inside the building.”

The air strike on the school occurred on the same day a suspected suicide bomber killed more than 20 people in an attack on a police bus in the heart of Kabul.

Other violence around the country made Sunday one of the bloodiest days since the Taliban were driven from power in 2001.

Read more at Reuters