Egyptian and Emirati influence on Donald Trump has thrown US policy on Libya into turmoil at a moment when Tripoli is under attack and the country is on the brink of a full-scale war once again.

The state department went from encouraging a UN security council resolution calling for a ceasefire and an end to an offensive on the capital by the eastern Libyan warlord, Khalifa Haftar, to threatening to veto the same resolution a few days later.

The sudden change of policy followed a Trump meeting with Egyptian leader Abdel Fattah al-Sisi, and a phone conversation with the Abu Dhabi crown prince, Mohamed bin Zayed Al Nahyan, Haftar’s principal backers.

They persuaded him to call Haftar and to then issue a statement praising him, diplomats and a former official said. According to Bloomberg news, Trump and his national security adviser, John Bolton, expressed support for Haftar’s offensive, directly contradicting a formal statement a few days earlier from the secretary of state, Mike Pompeo.

The state department has called for a ceasefire in Libya and a return to UN political mediation but the statement did little to clarify the confusion surrounding US policy in the wake of Trump’s personal gesture of support for Haftar.

“Lasting peace and stability in Libya will only come through a political solution. We call on all parties to rapidly return to UN political mediation, the success of which depends upon a ceasefire in and around Tripoli,” a state department spokesperson said in an emailed statement on Monday.

Libya is the latest in a long list of foreign policy and global security issues on which Trump has upended longstanding policy with little to no notice or consultation with allies or the rest of his administration.

On this occasion, Trump is reported by European diplomats to have abandoned the official US position of supporting the beleaguered UN-backed government in Tripoli and to urge UN-brokered mediation, in order to please Haftar’s Egyptian and UAE backers.

The US president is seeking to garner support from both states for a long-delayed Israeli-Palestinian peace plan being championed by his son-in-law Jared Kushner, due to be unveiled after the end of Ramadan in June.

According to diplomats briefed on the talks, Sisi used a White House visit on 9 April to ask for Trump to show support for Haftar, who he portrayed as leading the fight against terrorism in Libya.

Trump called Haftar on 15 April, but the White House kept the conversation a secret, one source said, until UAE’s Mohammed bin Zayed encouraged Trump to make his support public, to encourage defections of Libya’s many militias to Haftar’s cause. The White House issued an account of the conversation with the Libyan militia leader on 19 April, praising him for “his significant role in fighting terrorism”.

“The state department had no advance knowledge of the conversation, and there was no policy discussion,” a former official said. “The US now has no coherent policy on Libya because there has just been no policy review, just transactional behaviour by Trump’s family.”

In the days after the call, the US radically changed its position on Libya. The US mission at the UN threatened to veto a UK-drafted UN security council resolution calling for an end to Haftar’s offensive and an immediate ceasefire.

The threat came as a shock to US allies as the state department had, only a few days earlier, encouraged the UK to draft the resolution, and Pompeo had issued a formal statement opposing Haftar’s power grab.

“The green light had come from a senior official at state,” a European diplomat said. “There was a complete switch in the course of a week. From green-lighting it they went to completely opposing it. They weren’t saying: we think this is a bad idea. They said: we are going to veto this. We don’t want a resolution to go forward.”

The diplomat said the US was more adamant in its opposition than Russia, which had asked for amendments to make the resolution more “balanced” and less explicitly anti-Haftar, but did not go so far as brandishing a security council veto.

Asked about the administration’s foreign policy on Monday, the US national security council deferred to the state department, and issued a statement restating support for a ceasefire.

“Lasting peace and stability in Libya will only come through a political solution. We call on all parties to rapidly return to UN political mediation, the success of which depends upon a ceasefire in and around Tripoli,” a state department spokesperson said in an emailed statement.

There was no explanation however of US opposition to a UN resolution, or Trump’s open support for Haftar, who has US citizenship following a period of exile during the regime of Muammar Gaddafi, and who has been accused of war crimes.

Haftar’s offensive pre-empted and derailed a UN-brokered conference in the town of Ghadames organised by the UN special envoy for Libya, Ghassan Salamé.

Salamé warned against western support for Haftar during a visit to Paris. In an unusually forceful judgment for a UN mediator, he said: “He is no Abraham Lincoln, he is no big democrat … Seeing him act, we can be worried about his methods because where he is governing, he doesn’t govern softly, but with an iron fist.”

Few diplomats believed that a UN resolution would do much to stop the fighting on the ground, but many worry that the absence of a strong message from the international community, combined with apparent support from Trump, could lead to defections to Haftar’s ranks and hasten Tripoli’s fall.

Wolfgang Pusztai, a former Austrian defence attaché to Libya who is now a private security consultant, said the battle for the capital was finely balanced.

“It is at a tipping point,” said Pusztai, who is chairman of the advisory board of the National Council on US-Libya relations. He said Haftar’s forces were advancing on one front on the outskirts of Tripoli, but were stalled on another and were being pushed by a Misrata-based militia on a third.

Jonathan Winer, a former US special envoy for Libya, said a switch to a US policy supporting Haftar in the belief that he would be a reliable counter-terrorist ally, would have disastrous consequences.

“The risk here is that Libya winds up looking more like Syria with a broadening civil conflict, a large number of people fleeing, a humanitarian crisis and resurgent terrorism,” Winer said. “We need a political solution, not a military one.”