AMMAN (Reuters) – Four attackers who killed nine people in Jordan on Sunday had suicide vests and other weapons, Interior Minister Salamah Hamad said.

“This was a big terrorist operation but we are still in the stage of follow-up of information that relates to it,” Hamad told a news conference on Monday.

He gave no details on the identity or nationality of the attackers, saying investigations were continuing and disclosing details at this stage could hamper national security.

Jordanian security forces said late on Sunday they had killed four “terrorist outlaws” after flushing them out of a Crusader castle in the southern city of Karak. They had holed up there after killing a Canadian woman, three other civilians and five police officers.

The secrecy around the culprits, and whether they belonged to any militant group, has raised speculation from politicians and diplomats they could have been tribal outlaws with a grievance against the state rather than Islamic State fighters, who control parts of neighboring Syria and Iraq.

The security forces were able to release around 10 tourists. At least 30 people were hospitalized, some with serious injuries.

(Reporting by Suleiman al-Khalidi; Writing by Angus McDowall; Editing by Mark Trevelyan)