The new leader of Islamic State has been confirmed as Amir Mohammed Abdul Rahman al-Mawli al-Salbi, according to officials from two intelligence services. He is one of the terror group’s founding members and has led the enslavement of Iraq’s Yazidi minority and has overseen operations around the globe.

The Guardian has learned that Salbi was named leader hours after the death of Abu Bakr al-Baghdadi in October. The name that the group gave for Baghdadi’s replacement at the time, Abu Ibrahim al-Hashimi al-Quraishi, was a nom de guerre not recognised by other senior leaders or intelligence agencies.

In the three months since the raid that killed Baghdadi, a fuller picture of Salbi has been pieced together by regional and western spies, placing him at the centre of Isis decision-making – and that of its forerunners – and portraying him as a hardened veteran in the same vein as Baghdadi, unflinching in his loyalty to the extremist group.

Salbi is considered to be one of the most influential ideologues among the now depleted ranks of Isis. Born into an Iraqi Turkmen family in the town of Tal Afar, he is one of the few non-Arabs among the leadership.

He is also known by the nom de guerre Haji Abdullah, and in some circles as Abdullah Qardash – although Iraqi officials suggest the latter was a separate Isis figure who died two years ago.

Salbi, as intelligence officials now know him, rose through the ranks helped by his background as an Islamic scholar and gave religious rulings that underwrote the genocide against Yazidis and the emptying of the Nieveh Plains in northern Iraq during the height of the Isis rampage. Salbi holds a degree in sharia law from the University of Mosul. In 2004 he was detained by US forces in Camp Bucca prison in southern Iraq where he met Baghdadi. He is believed to have at least one son.

Before Baghdadi’s death in a US military raid in north-west Syria on 27 October, the US state department put a $5m bounty on Salbi’s head and on two other senior members of the group. Salbi was touted as a potential replacement for the ailing Baghdadi in August but confirmation of his appointment took several months to secure.

Since then he is understood to have been trying to consolidate the new Isis leadership, nearly all of whom apart from Salbi himself are drawn from a new generation who were too young to play roles in Isis’s founding battles against US forces from 2004 or in the Iraqi civil war that followed.

Isis is yet to regain anything like the juggernaut-like momentum that led to it threatening the regional order after Baghdadi proclaimed himself a caliph of the Islamic world in mid-2014. However, it has shown signs of regrouping since it lost its last foothold of land in the deserts of eastern Syria in March last year.

Kurdish forces in northern Iraq have warned since last summer of an increase in attacks in the centre and north of the country. Isis claimed to have carried out 106 attacks between 20 and 26 December to avenge the deaths of Baghdadi and the Isis propaganda chief, Abu Hassan al-Muhajir, on the same day.

A senior Iraqi Kurdish official said: “We’ve seen significant uptick in Isis attacks from mid last year, with the centre of gravity having now moved further south. We’re now tracking on average 60 attacks a month through assassinations, roadside bombs and assaults on Iraqi security forces.

“Their rural networks remain very much intact; after all, Isis members in Iraq still receive monthly salaries and training in remote mountainous areas. That network allows the organisation to endure, even when militarily defeated.”

The old city of Mosul, Iraq. The city has been a refuge for what remains of Isis’s leaders and rank and file. Photograph: Abdullah Rashid/Reuters

The hunt for Salbi has extended to Turkey where his brother, Adel Salbi, is a representative in a political party called the Turkmen Iraqi Front. The new Isis leader is thought to have maintained connections with his brother until he was named as leader.

Intelligence officials have little insight into his whereabouts but suggest he is unlikely to have followed Baghdadi to Idlib province and would have preferred to stay in a small band of towns to the west of Mosul.

The city of Mosul itself has been a refuge for what remains of the group’s leaders and rank and file, who have attempted to melt back into communities that are steadily rebuilding after five years of war and dislocation.

Another senior Isis figure who used religious credentials to offer rulings, Shifa al-Nima, was arrested last week in a Mosul suburb. He was taken to a detention centre on a flatbed truck as he weighed 254kg (nearly 40st) and was unable to walk.

Iraqi officials said Nima regularly ordered the execution of clerics and security officials who did not abide by the rigid decrees of the organisation.

Across the border in Syria, officials are still struggling to contain what British, French and other European officials regard as the biggest residual threat posed by Isis – two large detention centres set up to house members of the group and their families who fled its last redoubt.

Al-Hol and al-Roj camps, controlled by Syrian Kurdish forces, remain hotbeds of extremism. Corners of al-Hol camp in particular remain off-limits to security forces and there have been widespread reports of hardline religious instruction being given by female members of the group regarded as irreconcilables. Kurdish sources have spoken of indoctrination taking place and other members of the camp being intimidated and harassed by hardliners.

What to do with the foreign Isis prisoners in Syria, thought to number around 2,000, has vexed European officials who fear both a mass breakout from overstretched prisons and the political consequences of allowing citizens who had travelled to join Isis to return home.

Britain has stripped citizenship from several of its citizens, including Shamima Begum who fled the UK for Syria when she was 15. The US has done the same to Hoda Mothana, another so-called Isis bride, who was captured in western Syria in January last year.