"I won't call them monsters because they would like that term", Trump said in a joint news conference with Abbas on the second day of the USA president's two-day visit to Israel and the West Bank.
Speaking later alongside Israeli Prime Minister Benjamin Netanyahu at the Israel Museum in Jerusalem, Trump struck a more somber tone, offering his condolences to the victims and their families.
Trump said,"So many young lovely innocent people living and enjoying their lives murdered by evil losers in life".
Trump added that "I will call them from now on losers because that's what they are".
Police said the attacker detonated the explosives shortly after 10:33 p.m. on Monday, or 4:33 a.m. on Tuesday Western Indonesia Time, at Manchester Arena, as thousands of fans streamed out of a concert by USA singer Ariana Grande. I won't call them monsters because they would like that term.
In his remarks, Trump simply condemned the mastermind (s) behind the attack as "evil losers".
Melania Trump announces first overseas trip as first lady
But now he's on his way to Saudi Arabia, to Israel, to Rome, to Brussels and Sicily, with a hugely ambitious agenda. The president is scheduled to meet with the six-nation Gulf Cooperation Council, which is led by Saudi Arabia.
At least 22 people were killed as they exited a concert by the American pop star Ariana Grande at Manchester Arena.
While police believe the suspect was acting alone, investigations are ongoing to establish if he was part of a network.
Abbas also expressed his "warm condolences" to the victims of the attack and to the British people. This wicked ideology must be obliterated, and innocent life must be protected. And in today's attack it was mostly innocent children.
"Our society can have no tolerance for this continuation of bloodshed".
The White House said Trump was updated on the attack in Manchester, England by his national security team in Israel. This will easily go down as the worst attack in the history of Manchester, and authorities have confirmed that they are investigating it as a terrorist attack.