An aviation student from Saudi Arabia opened fire in a naval base classroom in Florida on Friday, local time, killing four people.
The shooting at a naval air station in Pensacola, Florida also injured 8 others, including two officers who were shot in the limbs.
The gunman, who was shot dead by police, has been named as Mohammed Saeed Alshamrani - a Saudi military pilot training at the site.
President Trump tweeted his condolences for the victims and their families.
He said that the government is monitoring the situation as the investigation is ongoing, but declined to say whether the shooting was terrorism-related.
The latest attack marks the second shooting at a U.S. military base this week.