After more than half a century in and around Libyan politics, and at the age of 75, Field Marshal Khalifa Haftar stands poised at the gates of Tripoli, as close to imposing a form of military rule across the country than at any time in his mercurial and often violent career.

It may yet be that his grandly titled Libyan National Army – a misnomer for a band of ideologically incoherent militias – will discover that it has overstretched itself, and his advance will be repelled. In a similar, less planned a ttempt by Haftar to seize power in 2014, he only partially succeeded, by taking control of Benghazi, the main town in the east of the country.

Even now, the UK Foreign Office is watching sceptically to see if the latest reports of his military advances denote groups swapping sides, or a decisive shift in the military and political balance.

But the UN secretary general, António Guterres, exited a meeting with Haftar in his stronghold in Benghazi on Friday clearly deeply depressed after failing to persuade the general to hold back from what could be a bloody battle for the capital. He said he left Libya “with a deep concern and a heavy heart” and voicing only hope that a “bloody confrontation” could be avoided. Haftar clearly feels militias will defect to him.

Nearly eight years after the Nato-backed toppling of the brutal dictatorship of Muammar Gaddafi, the oil-rich country may find itself once again under authoritarian rule, a replica of the regime of Gen Abdel Fattah el-Sisi in neighbouring Egypt.

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Critics such as Elham Saudi, the director of Lawyers for Justice in Libya, claim the international community – in an attempt to end the deadlock between the east and west of the country – have for too long sought to incorporate Haftar into Libya’s democratic process.

“The UN has consistently followed a policy of appeasement, and not of accountability,” she said. “Most of the statements from international bodies calling for restraint direct their appeal to both sides equally, rather than singling Haftar out as the aggressor.”

Only late on Friday, at the request of the UK, did the UN security council end its timidity and directly identify the LNA, calling on it “to end all military movements”.

That coyness may reflect the support Haftar has accumulated diplomatically in Egypt, the United Arab Emirates and parts of the French government.

Alternatively, it is a near-admission of defeat by western democracies that ultimately see their interests in Libya through the narrow prism of migration, counter-terrorism, and oil, rather than building a pluralist state in a country that has little history of democracy.

If the goal is security, stemming the flow of migrants to Italy, securing oil supplies and combatting Islamic State, some may see Haftar as the easiest solution. But that may underestimate the many reasons Haftar generates resentment in the west of Libya, especially in towns such as Misrata.

Haftar played a minor role in Gaddafi’s overthrow of the monarchy in 1969, and was subsequently trained in Cairo and Moscow, commanding the city of Tobruk from 1981 to 1986. He came to greater prominence as a general commanding Gaddafi’s forces in Chad in 1987, but was disowned by the dictator for his failures, including his capture.

Facebook Twitter Pinterest A video on the Libyan National Army Facebook allegedly shows military convoys heading towards Tripoli. Photograph: AFP/Getty Images

He then spent up to 20 years in exile in the US, living close to the CIA headquarters in northern Virginia, and allegedly being trained to prepare a counter-Gaddafi force by the Reagan administration. He was granted US citizenship, and many of his family still live there. In 2011, as the revolt against Gaddafi spread, he returned to Libya, playing a disputed role in the revolution.

Even though Haftar talks of purifying his country, he eschews the worst bombastic rhetoric of some leaders, preferring to couch his politics as a fight against terrorism and Islamists that he says have overridden the UN-recognised, but ineffectual, Tripoli Government of National Accord (GNA) of Fayez Mustafa al-Sarraj.

Although he says his foe is the Muslim Brotherhood and his cause secularism, he consorts with the Madkhalis, a Saudi-backed conservative sect. In those parts of the east he now rules, civilian administration has been replaced by the military.

Haftar’s health has been a matter of rumour, and when there were inaccurate reports of his death in a Paris hospital last year, infighting broke out among his entourage in a war of premature succession. There were even claims Haftar allowed the rumours of his demise to spread, to test the loyalty of his circle.

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But since 2011, he has doggedly rejected UN-brokered compromises, refusing to recognise the legitimacy of the GNA and demanding that he be given powers to run a unified army freed from civilian direction.

The laws of war are not closely followed in any part of Libya, but Human Rights Watch this week questioned the value of Haftar’s orders for civilians in Tripoli not to be targeted, saying: “Fighters under his command have been implicated in serious abuses against civilians elsewhere in the country, including preventing civilians from leaving areas under siege looting and burning homes, as well as carrying out summary executions.” Elham Saudi points out that although arrest warrants have been issued by the international criminal court for one of his commanders, Mahmoud al-Werfalli, he has been left untouched.

Critics also claim Haftar should never have been seen by the UN as someone that could be controlled or cajoled into political compromise. The international silence that met his rapid military advance cross southern Libya this year, including the capture of the giant el-Sharara and el-Feel oil fields, only encouraged him to press on to Tripoli.

The frustration for the UN was that, after a year of meticulous work, the country seemed closer to a political settlement than at any time for two years. A national reconciliation conference is due to meet in less than a fortnight’s time, but Haftar appears to have wanted to pre-empt its conclusions. Haftar’s advance has at least clarified he does not intend to be part of a brokered solution.