By Trevor Hunnicutt and Steve Holland

WASHINGTON (Reuters) -President Donald Trump sharply criticized Iran's Supreme Leader, Ali Khamanei, on Friday, dropped plans to lift sanctions on Iran and said he would consider bombing Iran again if Tehran is enriching uranium to worrisome levels.

Trump reacted sternly to Khamanei's first remarks after a 12-day conflict with Israel that ended when the United States launched bombing raids last weekend against Iranian nuclear sites.

Khamanei said Iran "slapped America in the face" by launching an attack against a major U.S. base in Qatar following last weekend's U.S. bombing raid. Khamanei also said Iran would never surrender.

Trump said he had spared Khamanei's life. U.S. officials told Reuters on June 15 that Trump had vetoed an Israeli plan to kill the supreme leader.

"His Country was decimated, his three evil Nuclear Sites were OBLITERATED, and I knew EXACTLY where he was sheltered, and would not let Israel, or the U.S. Armed Forces, by far the Greatest and Most Powerful in the World, terminate his life," Trump said in a social media post.

"I SAVED HIM FROM A VERY UGLY AND IGNOMINIOUS DEATH," he said.

Trump also said that in recent days he had been working on the possible removal of sanctions on Iran to give it a chance for a speedy recovery. He said he has now abandoned that effort.

"I get hit with a statement of anger, hatred, and disgust, and immediately dropped all work on sanction relief, and more," he said.

Trump said at a White House news conference that he did not rule out attacking Iran again when asked about the possibility of new bombing of Iranian nuclear sites if deemed necessary at some point.

"Sure, without question, absolutely," he said.

Trump said he would like inspectors from the International Atomic Energy Agency or another respected source to be able to inspect Iran's nuclear sites after they were bombed last weekend.

Trump said he believes the sites were "obliterated." He has rejected any suggestion that damage to the sites was not as profound as he has said.

But Trump said he would support the IAEA, the U.N. nuclear watchdog, going in to check the sites that were bombed.

The agency's chief, Rafael Grossi, said on Wednesday that ensuring the resumption of IAEA inspections was his top priority as none had taken place since Israel began bombing on June 13.

However, Iran's parliament approved moves on Wednesday to suspend such inspections. Iranian Foreign Minister Abbas Araqchi indicated on Friday that Tehran may reject any request by the head of the agency for visits to Iranian nuclear sites.

Trump also said he does not believe Iran wants to still seek a nuclear weapon after U.S. and Israeli bombing raids. He described Iran as "exhausted."

He said Iran still wants to meet about the way forward. The White House had said on Thursday that no meeting between the U.S. and an Iranian delegation has been scheduled thus far.

(Reporting by Trevor Hunnicutt, Steve Holland and Michelle Nichols; Editing by Franklin Paul, William Maclean, Alistair Bell and Sandra Maler)