The National Security Ministry said Monday it had thwarted a radical Islamic group's plot to conduct a "large-scale, horrifying terror attack" against government structures and diplomatic missions in the Azerbaijan capital, Baku.

It said that one suspect was killed and several others were detained in a weekend sweep outside the capital.

The British Embassy in Baku closed temporarily and the U.S. Embassy scaled back its operations in response to the threat.

The ministry said in a statement that the radical Islamic group included an army lieutenant who had stolen 20 hand grenades, a machine gun, four assault rifles and ammunition from his military unit and made them available for the planned attack.

Security forces tracked down the group and arrested several of its members during a sweep Saturday in the village of Mastaga about 30 kilometers (20 miles) northeast of Baku. One member of the group offered resistance to the arrest and was killed, the statement said.

"That prevented a large-scale, horrifying terror attack that was being prepared by members of this group against several state structures in Baku and embassies and missions of the countries which are members of the international anti-terror coalition," the ministry said in a statement.

It added that a hunt for other members of the group was still under way.

National Security Ministry spokesman Arif Babayev told The Associated Press that the radical Islamic group had planned to launch a "terror attack against several government structures in Baku and the U.S. Embassy."

The U.S. Embassy sent out an announcement to U.S. citizens saying it had closed its consular office for an indefinite period because of a security threat and said it encouraged Americans to "maintain a high level of vigilance."

Police cars were parked outside the embassy.

The British Embassy closed completely on Monday, according to a receptionist in the Landmark building where the embassy is located. No one answered the phone at the embassy.

Several offices in the Landmark building also shut down operations Monday, including included Norway's StatoilHydro ASA and BP Azerbaijan, the receptionist said.