In the wake of the attack Trump expressed his "deepest condolences" to the victims of the Manchester attacks, referring to those responsible as "evil losers in life".
Trump added that "I will call them from now on losers because that's what they are".
Children were among 22 people killed and dozens injured in the suspected suicide bombing on Monday night at a pop concert by United States star Ariana Grande in Britain's deadliest extremist attack in 12 years. "They would think that's a great name", Trump said.
The attack Monday came just a day after Trump addressed dozens of Arab and Muslim leaders in Riyadh, calling on them to help "drive out" terrorists and "obliterate this evil ideology".
The suicide bomber detonated an explosive device near an exit to the 21,000-person capacity Manchester Arena where USA pop star Ariana Grande was performing to a sold-out audience. "They are losers. We will have more of them, but they are losers, just remember that". The explosion killed 22 people and injured 59, according to Greater Manchester police.
"Our society can have no tolerance for this continuation of bloodshed".
The White House said Trump spoke with British Prime Minister Theresa May shortly after the attack, reassuring her that Americans stand with Britain and "will never waiver in the face of terrorism".
As many as 400 police were deployed overnight, Chief Constable Ian Hopkins said early Tuesday.
"The attacker, I can confirm, died at the arena".
If confirmed as a terror incident, it would be the deadliest attack on British soil since the 2005 London bombings, which killed 52 people.