KABUL (BNO NEWS) — An explosion at a U.S. base in eastern Afghanistan on Wednesday killed at least eight American civilians, officials said. Several media reports say the blast was caused by a suicide bomber.

The explosion, which took place just before 5 p.m. local time, happened at the Forward Operating Base in Afghanistan’s Khost province, according to NATO officials. NATO denied any American or international forces were killed or injured in the blast, but a high-ranking U.S. official confirmed to BNO News that at least eight Americans had been killed. The official did not know if they were military or civilian.

A report from the New York Times said at least six Americans were injured, but the U.S. official was not able to confirm that. It was not immediately clear what caused the explosion.

“We are careful in deciding what we are putting out because the families of the victims are currently being informed,” the official added.

The U.S. Embassy in Kabul confirmed there was an explosion at the base, but had no other details. U.S. Embassy spokesman Brendan O’Brien said more information was expected after 9.30 a.m. local time on Thursday. A report from the Dow Jones Newswire said the U.S. Embassy was preparing to hold a news conference on Thursday morning, but O’Brien said that was not the case.