Last-ditch appeals are being made to persuade Khalifa Haftar to step back from the brink of an all-out attack on Tripoli, Libya’s capital, after the UN security council warned him to halt all military manoeuvres and said those threatening military solutions would face consequences.

It is the first time the international community has been so clear that Haftar is responsible for the aggression and follows a failed effort by the UN secretary general, António Guterres, to persuade h im to hold mediation talks in Geneva with Libya’s prime minister, Fayez al-Sarraj.

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Haftar announced on Wednesday he was launching an assault on Tripoli, and diplomats fear the crisis is escalating out of control.

There is a lingering hope that Haftar misunderstood messages from key allies as giving him implicit blessing for his attack. The EU is making strenuous efforts to ensure that the US is seen to be telling Haftar to back off, and to tell his three principle external supporters – Egypt, Saudi Arabia and the United Arab Emirates – to do the same.

Haftar met King Salman of Saudi Arabia on 27 March in Riyadh. The king did not, however, meet with Sarraj at the Arab League meeting in Tunis two days later, a move that could be taken as a signal of support for Haftar at a time when it was known he was considering an attack on Tripoli.

It was also noted that Egypt did not put its name to a joint statement last week from the US, France, Italy, the UK and the UAE calling for restraint. Cairo has been one of Haftar’s strongest supporters.

Haftar’s troops are assembled in the Jufra area, and it is thought forces from the coastal town of Misrata, loyal to the government of Sarraj, are willing to stage attacks against him. As the military leader in the east, Haftar may not yet have secured the level of militia support he expected inside Tripoli, but one source said alliances were shifting by the hour.

Facebook Twitter Pinterest Khalifa Haftar (left) greets António Guterres on Friday. Photograph: Libyan Army Media Office/EPA

Haftar has insisted in talks with western diplomats, that he be allowed to take over as military leader at least until a new prime minister is elected and seems unwilling to backtrack on his demands, despite a direct warning by EU ambassadors not to take decisive military steps.

One source said they feared Haftar either misread sometimes conflicting messages from his external allies or chose to misread them. “He is largely a military figure, and the quality of political advice that he is receiving from his immediate circle is not that sophisticated,” they said. “No one can understand why he thought it was good politics to launch an attack on Tripoli in the middle of a two-day visit to Libya by the secretary general.”

The possibility of a UN-sponsored reconciliation conference going ahead as scheduled on 14 April hangs in the balance, with forces in Misrata, including the Libyan interior minister, Fathi Bashagha, seen as a moderate, furious at what he regards as a betrayal by Haftar.

One source said France, viewed as the strongest European partner of Haftar, may be nervous that he was out of control, and suggested the French president, Emmanuel Macron, would not want a transatlantic rift to develop over his support for an authoritarian leader in the middle of the European elections.