Donald Trump is facing mounting criticism after telling Fox News Iran was “probably” planning to attack four US embassies before he authorised the drone assassination of the top Iranian general Qassem Suleimani earlier this month.

Chris Murphy, a Democratic member of the Senate foreign relations committee, said: “Let’s be clear – if there was evidence of imminent attacks on four embassies, the administration would have said so at our Wednesday briefing. They didn’t. So either Fox News gets higher-level briefings than Congress ... or … wait for it ... there was no such imminent threat.”

The assassination of Suleimani was prompted in part by a rocket strike against a US base in Iraq that wounded troops and killed a civilian contractor. The death of Suleimani was answered by Iranian strikes on US bases in Iraq. Iran has also admitted shooting down a passenger jet by mistake, killing 176 people.

Timeline The buildup to Qassem Suleimani's death Show A rocket attack on an Iraqi military base near Kirkuk kills an American contractor and injures US and Iraqi soldiers. The US blames Shia militia group, Kata’ib Hizbullah (KH) The US conducts retaliatory airstrikes against five KH bases in Iraq and Syria, saying there had been 11 attacks against Iraqi bases hosting coalition forces in Iraq over the past two months Protesters storm the US embassy in Baghdad, trapping diplomats inside while chanting “Death to America” and slogans in support of pro-Iranian militias. At one point they breached the main gate and smashed their way into several reception rooms. The rampage was carried out with the apparent connivance of local Iraqi security forces who allowed protesters inside the highly protected Green Zone In a drone strike ordered by US president Donald Trump, the US kills Iranian general Qassem Suleimani while he was being transported from Baghdad airport

The Trump administration has said Suleimani was planning imminent attacks on US assets. But on Wednesday a congressional briefing, given amid attempts to rein the administration in, prompted rare bipartisan criticism.

Mike Lee, a Republican from Utah, said it was “not acceptable for officials within the executive branch of government … to come in and tell us that we can’t debate and discuss the appropriateness of military intervention against Iran. It’s un-American. It’s unconstitutional and it’s wrong.”

On Saturday, Lee announced he had partnered with the Vermont senator Bernie Sanders, a candidate for the Democratic presidential nomination, to co-sponsor legislation that would freeze funding for military action against Iran without approval from Congress.

In a joint statement, the Tea Party-backed Republican and the democratic socialist independent said: “We often disagree on many issues. But standing up for the constitution is not about partisanship. The founding fathers were absolutely clear. They wanted to ensure that our country avoided needless conflict and they understood that presidential war-making would be harmful to our democracy.”

Trump’s interview with the Fox News host Laura Ingraham was broadcast on Friday night. Asked what Iran had been targeting, he revisited remarks to reporters and at a rally on Thursday when he said: “We will tell you that probably it was going to be the embassy in Baghdad.”

That embassy was attacked by pro-Iranian groups on New Year’s Eve, another event contributing to Trump’s authorisation of the strike on Suleimani. Trump then told Ingraham he could “reveal that I believe it probably would’ve been four embassies”.

“[It] could have been military bases,” he said, “could have been a lot of other things too. But it was imminent, and then all of a sudden, he [Suleimani] was gone.”

The secretary of state, Mike Pompeo, told reporters on Friday the US “had specific information on an imminent threat, and those threats included attacks on US embassies period full stop”. Pompeo claimed “American facilities including American embassies, military bases, American facilities throughout the region” were at risk.

But the Washington Post cited “a senior administration official and a senior defense official” who said they “were only aware of vague intelligence about a plot against the embassy in Baghdad and that the information did not suggest a fully formed plot. Neither official said there were threats against multiple embassies”.

One official told the Post there was concern about a possible attempt to bomb the Baghdad embassy.

Responding to Trump’s interview, Murphy said he had “placed a request … for a briefing on the new intelligence surrounding the imminent attacks on US embassies that the president referred to today, but somehow didn’t come up in the full Senate briefing on Wednesday”.

Trump also told Fox News his “biggest thing” was not letting US enemies such as Iran have nuclear weapons.

The president withdrew from the Iran nuclear accord, meant to slow Tehran’s progress towards a weapon, in May 2018. After the strike on Suleimani, Tehran said it was ending commitments under the deal.

On Saturday the news site Axios reported that national security adviser Robert O’Brien said “the chances of sitting down with the Iranians and getting to a deal have improved significantly” because Soleimani was “off the battlefield”.

On Fox News, Trump was also asked about comments from Democrats including Pete Buttigieg, the former mayor of South Bend, Indiana who is showing strongly in the presidential primary, which implied the US was partly to blame for Iran shooting down the airliner bound for Ukraine.

“I think it’s just lowlife,” Trump said, calling Buttigieg a “lousy mayor of a place that is not doing well”.

Trump said he would be “OK” with US troops withdrawing from Iraq, as demanded by the Iraqi parliament after the Suleimani strike, leading to confusion over US plans before the administration confirmed troops would stay.

He claimed the Iraqi government was saying it wanted US troops out “publicly” but “they don’t say that privately”.

Defending his decision last year to remove US troops from the border between Turkey and Syria, which led to a Turkish incursion against Kurdish forces allied to the US in the fight against Islamic State, Trump insisted it “turned out to be such a successful move”.

“Look what happened,” he said. “They’ve been fighting over that border for a thousand years. Why should we do it? And then they say ‘he left troops in Syria’. Do you know what I did? I left troops to take the oil. I took the oil – the only troops are protecting the oil.”

US troops do remain stationed near oilfields in Syria, but “taking the oil”, repeatedly advocated by Trump, would be illegal under international law as applied and accepted around the world since 1945.

In the aftermath of the Suleimani strike, Trump repeatedly threatened to strike Iranian cultural sites, an act that would also have constituted a war crime. In the face of international criticism, the president climbed down.