U.S. officials say they believe the Pakistan-based Haqqani network was behind the powerful truck bomb blast at a NATO base in central Afghanistan that killed four Afghan civilians and wounded more than 100 others, including 77 U.S. troops.

The Taliban claimed responsibility for Saturday's attack outside the main gate of the Combat Outpost Sayed Abad in Wardak province. But Pentagon spokesman George Little said Monday there is a very strong likelihood that Haqqani leadership supported and was aware of the attack.

Spokesman for the Joint Chiefs of Staff, Navy Captain John Kirby said the attacker was not “some guy with a suicide vest.” Kirby said the bomber had “a large vehicle with a large amount of explosives” and that kind of attack could not be launched “without good resourcing, good planning and a fair level of coordination.”

The militant Haqqani network, which operates from Pakistan's North Waziristan tribal region and is affiliated with both the Taliban and al-Qaida, has launched a number of high-profile attacks in neighboring Afghanistan.

The explosion occurred on the eve of the 10th anniversary of the September 11 terror attacks against the United States.

Local officials said the brunt of the blast was absorbed by the protective barrier at the entrance, but about 100 shops in the area were damaged.