WASHINGTON, May 18 (Reuters) - President Donald Trump said on Monday there was a “very good chance” the United States could reach an agreement with Iran to prevent Tehran from obtaining a nuclear weapon, hours after saying he had postponed a planned military attack to allow negotiations to continue.

Trump said leaders from key U.S. allies in the Middle East had asked him to delay a planned military attack on Iran scheduled for Tuesday to allow negotiations with Tehran to continue, while warning the U.S. remained prepared to launch a large-scale assault if no agreement is reached.

"There seems to be a very good chance that they can work something out. If we can do that without bombing the hell out of them, I would be very happy," Trump told reporters gathered for a drug price announcement on Monday.

(Reporting By Steve Holland and Jarrett Renshaw; Editing by Caitlin Webber and Deepa Babington)