President Donald Trump said Tuesday that U.S. military officials advised him that a massive explosion in Beirut appeared to be an “attack,” though he offered little detail to explain how his administration had come to that conclusion.

At least 60 people were killed and thousands were wounded in an explosion that caused widespread damage in the Lebanese capital. Trump said he had been briefed by “our great generals” and that they “seem to feel” that the explosion was not an accident.

“According to them – they would know better than I would – but they seem to think it was an attack,” Trump told reporters at the White House. “It was a bomb of some kind.” The blast followed a fire that broke out in the city’s port area, based on multiple videos from the scene. “It looks like a terrible attack,” Trump said during his opening remarks.

“Our prayers go out to all the victims and their families,” he said. “The United States stands ready to assist Lebanon.” Though the cause of the explosion is yet to be officially determined, Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material that was stored at the port after it was confiscated from a ship. In a tweet on the Lebanese presidential account, the material was identified as ammonium nitrate, citing Prime Minister Hassan Diab as saying, “It is unacceptable that a shipment of ammonium nitrate estimated at 2,750 tons has been present for six years in a warehouse without taking preventive measures that endanger the safety of citizens.”