European divisions over how to respond to General Khalifa Haftar’s violent assault on the Libyan capital, Tripoli, have been exposed after France blocked a draft EU resolution that would have condemned him and called for him to retreat.

France, a supporter of the warlord over the past two years, blocked the draft despite new UN figures showing 56 reported dead, hundreds injured and more than 6,000 displaced by the fighting.

Haftar, whose power base is in the east of the country, says he is trying to oust the militias that dominate the UN-recognised government led by Fayez al-Serraj in Tripoli. Haftar’s critics claim he is bent on a violent coup, and will install a military dictatorship if successful.

The draft statement presented to EU leaders at their emergency Brexit summit in Brussels on Wednesday night said Haftar’s attack was “endangering the civilian population, disrupting the political process and risks further escalation with serious consequences for Libya and the wider region, including the terrorist threat”.

Q&A What is happening in Libya? Show Libya is on the brink of an all-out civil war that threatens to upend years of diplomatic efforts to reconcile two rival armed political factions. An advance led by Khalifa Haftar, the warlord from the east of the country, has diplomats scrambling and the UN appealing in vain for a truce. The French government, the European power closest to Haftar, insists it had no prior warning of his assault, which is closing in on the capital, Tripoli. The outcome could shape not just the politics of Libya, but also the security of the Mediterranean, and the relevance of democracy across the Middle East and north Africa. For more about the fighting in Libya read our quick guide. Photograph: Hani Amara/X03394

France may either be protecting their ally or judging criticism of him will reduce the EU’s ability to settle the crisis. French diplomats said they had only objected to the EU text because they wished to add specific extra elements designed to balance the statement.

One EU diplomat said: “The EU is focused on the same headline objective, but on the detail there is not yet consensus of approach between member states.”

At the UN in New York, a divided security council was briefed privately for two hours by the UN secretary general António Guterres and by video link from Tripoli by the UN special envoy Ghassan Salamé.

Guterres again called for a ceasefire. “It is clear that we have a very dangerous situation and it is clear that we absolutely need to stop the violence,” he said.

The UN as an institution is furious that Haftar’s attack came immediately before a carefully constructed national conference that was expected to see agreement reached next week on a new provisional government prior to elections at the end of the year.

Karen Pierce, the UK ambassador to the UN where the UK is the penholder on Libya, said: “There is no military solution to this conflict. There needs to be an inclusive political settlement and all sides need to cooperate with the United Nations in bringing about that inclusive political settlement.”

When asked if she thought it would be helpful to identify Haftar’s culpability, she said the focus should be on what is effective.

The UK has privately been discussing the imposition of UN sanctions against Haftar, but there is unlikely to be consensus. Diplomats who warned Haftar against an attack weeks ago admit they either misread his intentions or did not spell out the consequences forcefully enough.

Among a string of phone calls to Serraj, the international criminal court prosecutor Fatou Bensouda vowed the ICC would not be negligent in pursuing those guilty of war crimes especially if they had targeted civilian installations. One prominent member of Haftar’s self-styled Libyan National Army is already subject to an ICC arrest warrant, but he has not been handed to the ICC by Haftar.

The Libyan interior minister, Fathi Bashagha, and a past critic of the militia’s excessive influence on the GNA, appealed for the UN to be more active.“We are not going to sit idly by to see millions of children, women and elderly people intimidated by Haftar’s attacks and shelling.”

He indicated that they had captured underaged boys used by Haftar in his attacking forces as “mercenaries”.

In an update, the UN Office for the Coordination of Humanitarian Affairs said: “Heavy armed clashes and artillery shelling on residential areas in Ain Zara and Khalla alForjan have translated into an upsurge in displacement numbers in and around Tripoli, which doubled over the past 48 hours to just over 6,000 individuals.

“Due to ongoing conflict, access restrictions and indiscriminate targeting of first responders, only 58 out of 580 families who registered for evacuations from areas particularly affected by hostilities could be brought to comparatively safer places to date.

Writing in the Financial Times, Peter Millett, the former UK ambassador to Libya, accused Haftar of destroying Libya’s best chance of peace.

He wrote: “General Haftar cannot win. While he has quite a lot of tacit support in Tripoli from citizens who loathe the militias and want security, there is enough armed opposition to cause a bloodbath … To prevent a prolonged civil war, his backers and friends need to persuade him to pull back and return to the negotiating table. But that will not be easy.”