KABUL, Afghanistan — A suicide bomber detonated a truck loaded with explosives at a U.S. military outpost on Saturday, the eve of the 10th anniversary of the 9/11 terrorist attacks, NATO announced Sunday.

Two Afghan civilians were killed in the blast, which also wounded 77 NATO soldiers and about two dozen Afghan civilians.

NATO did not disclose the nationality of the wounded troops, but officials in Washington said they were all Americans. NATO, however, sought to play down the impact of the explosion on Combat Outpost Sayed Abad, which is located in Wardak province about 30 miles west of Kabul, Afghanistan’s capital.

None of the wounded soldiers suffered life-threatening injuries and most were expected to return to duty “shortly,” NATO said.

But accounts from Afghan officials suggested that a catastrophe had been narrowly averted as the United States was preparing for a day of solemn ceremonies commemorating the Sept. 11, 2001, terrorist attacks.

Alam Gul, a local council chief who lives about six miles from the site of the explosion, said he heard the blast from his home.

“The houses that were near the base have been badly damaged,” he said.

Gul said the truck’s explosive cargo had been hidden beneath a load of firewood. Shahidullah Shahid, a spokesman for the Wardak governor, said officials did not know how much of the explosives the truck was carrying.

NATO said the attack took place at around 5:30 p.m. Saturday, but provided few details. Most of the explosion’s force was absorbed by blast walls, NATO said, adding that damage was limited to the base’s perimeter wall and a “maintenance facility.”

The base “remains operational and the protective barriers have been repaired,” NATO said.

The Taliban took responsibility in a statement posted on their website. The posting claimed that 50 U.S. soldiers had died. The exaggeration was typical of Taliban announcements.

The Sayed Abad district is the same area where 30 American special forces troops and eight Afghan soldiers were killed last month when the Chinook helicopter they were riding in was shot down by Taliban insurgents.

Wardak province has witnessed growing Taliban activity in the last two years, and the attack was a reminder that 10 years after invading U.S. troops helped oust the Taliban regime, security remains precarious in most of Afghanistan.