National Security Adviser Robert O'Brien appeared on "Justice with Judge Jeanine" on Saturday and defended President Trump's decision to order an airstrike that killed Iranian general Qassem Soleimani Thursday in Baghdad, elaborating on the president's earlier tweets promising to "hit" 52 Iranian targets if Iran chooses to retaliate.

"The president takes threats made to the United States and threats against American citizens, our soldiers, sailors, airmen, Marines and diplomats, very seriously," O'Brien told host Judge Jeanine Pirro. "And I think the president is trying to make it clear to the Iranians that this is a very bad path for them to go down."

"We caught Qassem Soleimani in the act of planning and plotting to kill Americans in the region was eliminated in a precise operation carried out by the U.S. military. And we've said, hey, that's the end of it," O'Brien added.

TRUMP ORDERS ATTACK THAT KILLS IRANIAN GEN. QASSIM SOLEIMANI, OTHER MILITARY OFFICIALS IN BAGHDAD, PENTAGON SAYS

"Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have targeted 52 Iranian sites," Trump tweeted Saturday, saying that Iran "WILL BE HIT VERY FAST AND VERY HARD" and explicitly laying out that the U.S. will act if Iran retaliates.

O'Brien called the information surrounding possible attacks by Soleimani "very solid," saying the Iranian general planned to attack Americans with Iranian "proxy allies" in Syria, Lebanon and Iraq.

"Well, of course, we can't go into sources and methods, but I can tell you it was very solid intelligence," O'Brien said. "Soleimani was traveling around the region, working out a plan to attack Americans with his proxy allies, with Iran's proxy allies in Syria and Lebanon and in Iraq."

The White House official defended the president's actions, calling Soleimani a "terrorist leader," and defended the administration against criticism that they should have notified Congress before ordering the airstrike.

"What I'll say is that this is common practice in these sorts of operations," O'Brien said. "The president made a war powers notification to Congress today of the War Powers Act within the 48-hour period and we'll continue."

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"We feel very good about the legal basis for this, this military operation," O'Brien later added, saying it was an "absolutely legal operation" that "was signed off on by administrative lawyers at [the Justice Department] and otherwise."

Once again, O'Brien warned Iran that the matter was resolved as far as the U.S. was concerned before reiterating "there will be severe consequences" if they retaliate.