PALM BEACH, Florida (REUTERS) - President Donald Trump said on Friday (Jan 3) he ordered the killing of Qassem Soleimani to stop a war, not start one, saying the Iranian military commander was planning imminent attacks on Americans.

"Soleimani was plotting imminent and sinister attacks on American diplomats and military personnel but we caught him in the act and terminated him," Trump told reporters at his Mar-a-Lago resort.

"We took action last night to stop a war. We did not take action to start a war," Trump said, adding that the United States does not seek regime change in Iran.

Earlier, Trump said that Soleimani, the head of Iran's elite Quds Force, was responsible for killing and wounding "thousands" of Americans and many more in the region.

"He should have been taken out many years ago," Mr Trump tweeted from his private club in Palm Beach, Florida, where he was vacationing.

The strike marked a major escalation in the conflict between Washington and Iran, as Iran vowed "harsh retaliation" for the killing of the senior military leader.

The two nations have faced repeated crises since Mr Trump withdrew from the 2015 nuclear deal and imposed crippling sanctions.

The United States urged its citizens to leave Iraq "immediately" as fears mounted that the strike and any retaliation by Iran could ignite a conflict that engulfs the region.

Mr Trump opted not to play a round of golf on Friday, and he was not expected to be seen publicly until he travels to Miami for an afternoon event for his reelection campaign.