Washington — President Trump added a new piece of information to his administration's justification for the deadly strike to kill Iran's top military leader, Major General Qassem Soleimani, claiming Iran was planning to "blow up our embassy" in the days before his death.

At an unrelated event at the White House, reporters pressed him on complaints by members of Congress, including some Republicans, that administration officials who briefed lawmakers on Wednesday had failed to provide sufficient justification for the strike and had chided members for debating the matter.

"We did it because they were looking to blow up our embassy," the president said, presumably referring to the U.S. compound in Baghdad, which was the focus of angry protests by pro-Iranian demonstrators less than two weeks ago. The administration has claimed Soleimani was planning an "imminent" attack to kill Americans but has declined to elaborate on specific plots or the intelligence underpinning their assertions, saying that doing so would compromise intelligence sources and methods.

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"We also did it for other reasons that were very obvious," Mr. Trump continued. "Somebody died, one of our military people died, people were badly wounded just a week before. And we did it."

But the administration has yet to clarify the president's claim that Iran or Soleimani specifically was planning to blow up the embassy, and it's unclear exactly what he meant. Two sources familiar with Wednesday's briefing said there was no mention of Iran "looking to blow up our embassy," as the president said. Senator Richard Blumenthal, a Democrat from Connecticut, said the president's claim is inconsistent with what they were told behind closed doors.

"The Trump Administration keeps Congress & the American people in the dark under the guise of 'classification' & then the President throws it away—making a claim inconsistent with the meager information provided at yesterday's Senate briefing," Blumenthal said in a tweet attached to an article of Mr. Trump's embassy claim.

Secretary of Defense Mark Esper has said the "imminent" threat to American lives was "days" away from taking place when the U.S. took out Soleimani. Secretary of State Mike Pompeo said earlier in the week that Soleimani's actions in the days leading up to his death provided justification for the strike.

Democratic members of Congress and at least two Republicans, Senators Mike Lee and Rand Paul, left Wednesday's briefing with top administration officials on Capitol Hill feeling dissatisfied with the level of information provided.

"We were brought into this briefing today to talk to us about that attack on Friday," Lee told reporters on Wednesday. "I had hoped and expected to receive more information outlining the legal factual and moral justification for the attack. I was left somewhat unsatisfied on that front. The briefing only lasted 75 minutes whereupon our briefers left. This however is not the biggest problem I have with the briefing, which I would add was probably the worst briefing I've seen at least on a military issue in the nine years that I've served in the United States Senate."

As the president was speaking, CBS News reported that U.S. officials are confident that Iran was responsible for shooting down a Ukrainian passenger plane that came down shortly after leaving Tehran earlier this week. Mr. Trump said he knew little about the matter.

"Well, I have my suspicions," the president said. "It was flying in a pretty rough neighborhood, and somebody could have made a mistake. Some people say it was mechanical. I personally don't think that's even a question, personally."

Arden Farhi contributed to this report.