WASHINGTON (AP) — U.S. officials said Wednesday there is no indication the massive explosion in Lebanon that killed at least 100 people was an attack, contradicting President Donald Trump who said American generals told him it was likely caused by a bomb.

The officials, speaking only on condition of anonymity to discuss internal assessments, said that while it was not out of the realm of possibility that the blast was deliberately caused, the belief so far was that it was most likely an accident.

From the outset, U.S. officials have said that they did not know the cause of the initial fire and explosions that set off the larger blast. But they say they do believe the reports out of Lebanon claiming a large stockpile of ammonium nitrate left over from a seizure is what exploded.

On Tuesday, Trump said, "It looks like a terrible attack."

Trump was asked why he called it an attack and not an accident, especially since Lebanese officials said they had not determined the cause of the explosion. He told reporters at the White House: "It would seem like it based on the explosion. I met with some of our great generals and they just seem to feel that it was. This was not a — some kind of a manufacturing explosion type of a event. ... They seem to think it was an attack. It was a bomb of some kind, yes."

From video and other evidence, experts suggest that fireworks and ammonium nitrate were the fuel that ignited the explosion that rocked the Lebanese capital. The scale of the damage — from the area of the explosion at the port of Beirut to the windows blown out miles away — resembled other blasts involving the chemical compound commonly used as an agricultural fertilizer.

The compound typically does not detonate on its own and requires another ignition source. That likely came from a fire that engulfed what initially appeared to be fireworks stored at the port. The Lebanese government said it was putting an unspecified number of Beirut port officials under house arrest pending an investigation into how 2,750 tons of ammonium nitrate came to be stored at the port for years.

The U.S. Embassy in Beirut said at least one American citizen was killed and several more were injured in the explosion. "We are working closely with local authorities to determine if any additional U.S. citizens were affected," the embassy said in a statement Wednesday. The embassy said all of its employees are safe and accounted for.

Secretary of State Mike Pompeo spoke Wednesday with Lebanon's Prime Minister Hassan Diab to convey U.S. condolences to the Lebanese people, according to State Department deputy spokesperson Cale Brown.