The two Kuwaitis who attacked U.S. Marines this week were part of a group that planned more assaults on Americans, an Interior Ministry official said Friday.
However, no connection with Usama bin Laden's Al Qaeda terror network has been established yet, the official said on condition of anonymity.
Questioning of some 60 suspects and witnesses since Tuesday's shooting that killed one Marine and injured another have led to a "cell of around 15 people" that was headed by Anas al-Kandari, one of the attackers, the official said.
Al-Kandari, 21, and his 26-year-old cousin, Jassem al-Hajiri, both Muslim extremists who trained and fought in Afghanistan, drove up and opened fire on Marines taking a break from urban assault training on the island of Failaka, 10 miles off the coast of Kuwait City.
One Marine was killed and a second was wounded. The attackers then drove to a second location and attacked again before being killed by Marines.
"Yes, there is a group behind Anas and Jassem ... and they were planning other operations including some against American installations that could have been the embassy and housing of personnel connected to the military," the Interior Ministry official said.
The official confirmed the attackers trained in Afghanistan but said, "So far, there has been no proof of their connection to Al Qaeda."
The government has called the attack a "terrorist act."
The violence has startled many in Kuwait, a close U.S. ally where people generally consider the United States a friend that liberated their country from Iraqi occupation in the 1991 Gulf war.
The Pentagon identified the slain Marine as Lance Cpl. Antonio J. Sledd, 20, of Tampa, Fla. The wounded soldier was Lance Cpl. George R. Simpson, 21, of Dayton, Ohio. Both men were assigned to the 11th Marine Expeditionary Unit at Camp Pendleton, Calif.