BEIRUT — Syria's official news agency and activists say a suicide bombing has targeted a security building at the northeastern, mostly Kurdish city of Hassakeh.

The agency says there are casualties from Friday's attack, but gave no figures. The Britain-based Syrian Observatory for Human Rights says at least 20 troops were killed and the Criminal Security department building was badly damaged.

No one immediately claimed responsibility for the attack, which bore the hallmarks of the Islamic State group.

IS launched a surprise attack on Hassakeh on Thursday, capturing parts of the city.

The Observatory, which relies on a network of activists across Syria, says IS positions inside and around the city have been coming under intense airstrikes by the U.S.-led coalition over the past two days.