The US president made the remarks in a press briefing at the White House. It followed a series of massive explosions in Beirut that killed at least 78 people and injured over 4,000. The explosions took place near the Lebanese capital’s main port.
Mr Trump told reporters at the White House the US stands ready to support Lebanon after the explosions, but claimed it was an “attack”.
He said: “It looks like a terrible attack. It would seem like it, based on the explosion.
“I met with some of our great generals and they just seemed to feel that it was.”
Mr Trump added that his generals have dismissed that it was “some kind of a manufacturing explosion”, adding it was an intentional incident.
He said: “It was a bomb of some kind, yes.”
It is the first time the Lebanese explosions has been referred to as an attack.
Lebanon’s Prime Minister Hassan Diab blamed the explosions on 2,750 tonnes of ammonium nitrate stored at the Beirut port.
The agricultural fertiliser had been stored at a port-side warehouse in the city for six years.
Mr Diab has said that the “catastrophe” was a “ disaster in every sense of the word”, and has vowed punishment for those responsible.
He added: “What happened today will not pass without accountability. Those responsible for this catastrophe will pay the price.”
During the conference, Mr Trump also committed to aiding Lebanon.
He said: “Our prayers go out to all the victims and their families. The United States stands ready to assist Lebanon.
“We have a very good relationship with the people of Lebanon and we will be there to help.”
The explosions in Beirut have levelled the industrial ports for the city.
The full force of the blast, likened to a “nuclear bomb” detonation, was felt miles away, with houses taking damage outside the blast zone.
Residents said glass was broken in houses from Raouche, on the Mediterranean city’s western tip, to Rabieh six miles east.
Beirut’s main airport, six miles away from the port, was reportedly damaged by the explosion, with pictures showing sections of collapsed ceiling.
The US embassy has warned residents “There are reports of toxic gases released in the explosion”, and has advised people to stay indoors and wear masks.