WASHINGTON (REUTERS) - US President Donald Trump clearly had authority to kill Qassem Soleimani, US Attorney General William Barr said on Monday (Jan 13), adding that the White House consulted with his department before the strike on the Iranian commander.

Barr told reporters that Soleimani was a "legitimate military target" and the strike was a "legitimate act of self-defence."

"The Department of Justice was consulted and frankly I don't think it was a close call," Barr said. "I think the president clearly had the authority to act as he did under numerous different bases. We had a situation where the Iranians had already embarked on a series of escalating violent action taken against our allies, taken against the American people, our troops, with the avowed purpose of driving us out of the Middle East."

Since the Jan 3 strike that killed Soleimani, critics have questioned the Trump administration's assertion that Soleimani was planning an imminent attack against the United States, the timing of the strike, coordination within the administration and Trump's decision not to notify Congress, which holds the power to declare war, of his plans.

Earlier on Monday, Trump brushed aside many concerns, in a tweet saying it "doesn't really matter" if a threat was impending.

"The general in charge of these efforts, Soleimani, was clearly a legitimate military target. We had a very brief window of time to carry out the attack," Barr said. "This was a legitimate act of self-defence because it disrupted ongoing attacks that were being conducted - a campaign against the Americans - and it re-established deterrence."

Earlier on Monday, Trump on Monday morning defended his decision to kill Soleimani, contending Soleimani posed an impending threat to the United States but also saying that was not important given the military leader's history.

"The Fake News Media and their Democrat Partners are working hard to determine whether or not the future attack by terrorist Soleimani was 'imminent' or not, & was my team in agreement." Trump wrote on Twitter.

"The answer to both is a strong YES, but it doesn't really matter because of his horrible past!"

Since confirming that Iranian military leader Qassem Soleimani had been killed in a US air strike in Baghdad, administration officials have claimed they acted because of an imminent risk of attacks on American diplomats and service members in Iraq and throughout the region.

Democrats and a few Republicans in Congress have questioned the justification of the attacks and said they have not been given adequate, detailed briefings.

Last week Trump posited in an interview that Iran had been poised to attack four American embassies before Soleimani was killed in a US drone strike on Jan 3.

But on Sunday US Defence Secretary Mark Esper said he did not see specific evidence that Iran was planning an attack.

"What the president said was that there probably could be additional attacks against embassies. I shared that view," Esper said. "The president didn't cite a specific piece of evidence."

When pressed on whether intelligence officers offered concrete evidence on that point, Esper said: "I didn't see one with regards to four embassies."