President Trump announced on Saturday that the U.S. military had bombed three of Iran’s nuclear sites, including its uranium-enrichment facility deep underground at Fordo, injecting the United States directly into a war in the Middle East.

The president made the announcement on his social media website, Truth Social, shortly before 8 p.m. in Washington.

“We have completed our very successful attack on the three Nuclear sites in Iran, including Fordow, Natanz, and Esfahan. All planes are now outside of Iran air space,” the president wrote. “A full payload of BOMBS was dropped on the primary site, Fordow. All planes are safely on their way home. Congratulations to our great American Warriors. There is not another military in the World that could have done this. NOW IS THE TIME FOR PEACE!”

The bombing came two days after the White House said Mr. Trump would make a decision “within two weeks” about whether to move ahead with such an attack. Israeli officials were told about the bombing beforehand, and Mr. Trump spoke with Prime Minister Benjamin Netanyahu of Israel afterward, according to a person with knowledge of the conversations who spoke on condition of anonymity because they were not authorized to speak publicly.

Mr. Trump said he would address the nation on Saturday night from the White House at 10 p.m.

It was not immediately clear how many bombs were dropped, or how much damage was caused to Iran’s capacity to enrich uranium and potentially pursue a nuclear weapon. And Mr. Trump, who had been debating whether to join Israel’s war against Iran, immediately suggested that a diplomatic resolution was still possible. But it was far from clear that Iran would be interested in that.

Since making clear that he was considering striking Iran, Mr. Trump has faced pressure from Republican critics and supporters of such of a move, highlighting a split within his own party.