BEIRUT - The military chief and several top commanders of the Al-Qaeda-affiliated Al-Nusra Front have been reported killed in northwestern Syria, where the jihadist militia has been making major gains in recent months.

Syrian state media, a monitoring group and a local activist reported that Abu Hammam al-Shami had been killed but information on the circumstances of his death was contradictory.

Official Nusra sources did not announce the death of the jihadist, who is believed to have fought with Al-Qaeda in Afghanistan.

“Shami... was killed with a number of other leaders during a special operation by the army” in Idlib province, Syrian state news agency SANA reported, without specifying a date.

Rami Abdel Rahman, the head of the Syrian Observatory for Human Rights monitoring group, also said the commander had been killed but that the circumstances of his death were unclear. “Shami died of injuries on Thursday, but it is not clear when he sustained them,” Abdel Rahman told AFP. He said Shami may have been one of five Nusra leaders wounded in an air strike on Idlib province on February 27 by the US-led coalition attacking jihadists in Syria. An official Nusra statement that day named two commanders killed in that strike but did not mention Shami.  Local Syrian activist Ibrahim al-Idlibi told AFP Shami had been killed in that raid but that Nusra had not published his name due to the “sensitivity” of the information.

Reports of Shami’s death came as the Al-Qaeda affiliate consolidates gains in northern Syria.

Already the most powerful military force in Idlib province, Nusra dealt a major blow to one of its rivals - the Western-backed Hazm movement - at the weekend when it seized Hazm’s base in Aleppo province.

Nusra also claimed to have led a spectacular assault against a regime intelligence headquarters in Aleppo city on Wednesday, blowing up a tunnel near the building before storming the surrounding area.

Attacks on the group’s leadership are “an indication of the rising strength and influence of Nusra on the ground in Syria in recent months,” said Lina Khatib, director of the Carnegie Middle East Centre think tank.

“Because it operates in a decentralised manner, not top down, the loss of a leader is something that Nusra can recover from with minimal damage,” she said.

But Idlibi, the local activist, disagreed.

“It’s a definite hit to the morale of Nusra’s supporters,” he said. He said there were rumours of serious internal disputes within Nusra’s ranks regarding an apparent Qatar-led proposal for Nusra to split off from Al-Qaeda.

“They want to turn it into something like the Taliban - into a political movement,” he said.

Idlibi said Nusra political chief Abu Mohamed al-Jolani is in favour of the split, while Shami was against it.

Nusra has emerged as the most powerful jihadist group in northwestern Syria and, as well as fighting President Bashar al-Assad’s regime, has clashed with moderate rebels and its jihadist rival the Islamic State group.

Shami is reported to have travelled to Afghanistan in the late 1990s and was eventually put in charge of Syrian jihadists there. He later spent five years in prison in Lebanon, before travelling to Syria and joining Nusra.

Meanwhile, the European Union imposed additional sanctions against Syria on Friday, targeting backers of President Bashar al-Assad as the bloody conflict gets worse with no prospect of a peace deal.

“Seven persons and six entities providing support to the Syrian regime as well as benefitting from it have been targeted,” a statement said. “This brings the number of persons and entities targeted by EU sanctions over the violent repression against the civilian population in Syria to 218 persons and 69 entities,” it said.

The move follows a December decision to extend the sanctions regime to hit Assad and his supporters.

The European Union will publish the names of the individuals and entities in its Official Journal on Saturday, bringing the measures into effect. More than 220,000 people are believed to have died in Syria since a March 2011 popular uprising against Assad turned into a bloody sectarian conflict which has displaced millions and destroyed much of the country.