BEIRUT: A senior figure in an Al-Qaeda-linked group in Syria has been killed in a bloody dispute with rebel factions that has raged for more than three weeks across opposition-held parts of the country, activists and an Iraqi intelligence official said Monday.

Heavy fighting between the Islamic State of Iraq and Greater Syria (ISIS) and rival rebels has left more than 1,400 people dead across the country since Jan. 3, erupting after months of growing resentment against ISIS’ heavy-handed tactics in the territory under its control.

The senior militant, an Iraqi who went by the nom de guerre of Haji Bakr, was killed earlier this month in the town of Tal Rifaat in the northern province of Aleppo, according to the Britain-based Syrian Observatory for Human Rights monitoring group. That corresponded to reports provided by two activists based in the city of Aleppo, Hasan Kattan and another who spoke on condition of anonymity for security reasons.

A senior Iraqi intelligence official who specializes in Al-Qaeda said Haji Bakr was assassinated in a killing tied to the dispute between ISIS and armed opposition groups.

The official, who spoke on condition of anonymity because he was not authorized to brief the media, said Haji Bakr’s real name was Samir Abid Mohammad al-Halefawi, and that he served as an air defense officer in Saddam Hussein’s army before joining Al-Qaeda in Iraq after the 2003 U.S.-led invasion.

Haji Bakr supervised a series of attacks against hotels and embassies in Iraq in 2010, and headed the military council of Al-Qaeda in Iraq after the group’s then-leader, Abu Omar al-Baghdadi, was killed in 2010, the official said.

Haji Bakr had almost no public profile before a few weeks ago as rumors of his death spread.

Aymenn al-Tamimi, an expert on militant groups at the Middle East Forum, said it was not surprising that Haji Bakr was little known, saying the Islamic State “is very low profile about who’s at the very top of their leadership.”

“You could ask people within ISIS and they couldn’t tell you,” Tamimi said.

A little-known Islamist rebel group active in rural Aleppo issued a statement containing photographs of Haji Bakr’s body, along with a claim of responsibility.

Also in Aleppo province, pro-opposition news websites said that at least two high-ranking ISIS members had been captured by rebels during fierce fighting for the town of Hreitan. Four ISIS militants and three rebels were killed in the fighting, according to the Observatory.

They said that one of the two captured leaders was named Ahmad Jamal Nayef, and served as an “emir” for the area, north of Aleppo.

In the city, a roadside bomb targeting the headquarters of Islamist rebels claimed the life of a young boy, the Observatory said.

Clashes between ISIS and rebel groups were reported in several areas around the town of Safira, southeast of the city, while to the north, in the town of Al-Bab, pro-opposition news websites said that ISIS militants were cementing their control over the town by seizing the homes of civilian activists, confiscating the contents of currency exchange shops, and absconding with funds held by the town’s Shariah Committee.

On the Turkish border to the east, ISIS militants raised their flags in the village of Tal Abyad – ISIS has been chased out of much of the territory it controlled in Aleppo and Idlib provinces, but has mounted a defense in areas further to the east, such as Raqqa, and Tal Abyad.

Elsewhere, fighting between regime forces and rebel groups continued in several provinces, and was punctuated by a suicide car bomb blast that killed an unknown number of regime troops in rural Hama. The Observatory said a Saudi national with the Nusra Front group carried out the attack.

It said that in the village of Jabbata in Qunaitra province, a local rebel commander was killed by regime shelling, while in the eastern province of Deir al-Zor, the body of another local rebel commander was discovered, after it had been dumped in the Euphrates River.

The Observatory said that Sunday’s nationwide death toll stood at 158 people, which included 10 people who died of malnutrition in regime-blockaded areas.