The assassination of Abu Khalid al-Suri -- personal representative of al-Qaida chief Ayman al Zawahiri -- in northern Syria this week is expected to intensify fierce infighting between jihadist groups that's seriously weakening the rebellion against the regime of President Bashar Assad.

Suri, a Syrian jihadist icon and longtime associate of Osama bin Laden, was killed Sunday with five followers in a suicide bombing by the Islamic State of Iraq and the Levant near the embattled city of Aleppo, Suri's birthplace, his group said.

The attack at Suri's headquarters took the war between the extremist ISIL and the al-Nusra Front, its mainstream jihadist rival and considered al-Qaida's Syrian wing, to a new level as the fighting spread across northern Syria.

On Tuesday, al-Nusra Front's leader, Abu Mohammed al-Golani, gave ISIL five days to ends its war with other rebel groups or face a concerted campaign against it.

"If you refuse God's ruling, and not cease afflicting the Muslim community, it will act against this aggressive, ignorant way of thinking and banish it -- even from Iraq," Golani vowed in a statement monitored by the BBC.

More than 2,300 rebels have been killed in the internecine bloodshed of recent weeks, one the bloodiest episodes in a ferocious and increasingly complex civil war that begins its fourth year March 12.

The current phase erupted Feb. 2 after Zawahiri, who took over as leader of al-Qaida following the assassination of bin Laden by U.S. Special Forces in May 2011, denounced ISIL for its brutality, particularly against civilians, after months of quarreling between the group and other jihadist organizations.

Zawahiri, an Egyptian based in northern Pakistan, formally disowned ISIL, founded by Iraqi veteran Abu Bakr al-Baghdadi, declaring "it is not a branch of the al-Qaida group."

In a statement posted on several jihadist websites, Zawahiri said: "We do not have an organizational relationship with it, and are not responsible for their actions."

"The rebellious ISIL is not likely to dissolve itself ... and Baghdadi seems unlikely to back down," observed Brian Michael Jenkins of the RAND Corp. in an analysis published by The Daily Star newspaper of Lebanon Wednesday.

"Now that al-Qaida has declared ISIL a renegade, however, its leaders cannot allow ISIL to succeed in creating a rival center of power. That sets up a showdown that could turn an internal dispute into a schism that cuts across the jihadist universe."

With Suri murdered, "Baghdad must worry about his own survival. Now that he's no longer al-Qaida's man, his own lieutenants may feel free to challenge his leadership."

ISIL's savagery alienated many Syrian Muslims and Zawahiri, who years ago sought to rein in Baghdadi's bloodthirsty predecessor, the Jordanian Abu Musab al-Zarqawi, in Iraq for the same reasons.

Suri, a veteran of the jihadist wars in Afghanistan and Iraq, headed a Salafi group called Ahrar al-Sham and was allied with the al-Nusra Front, or the Victory Front.

Western intelligence services consider al-Nusra, which emerged in Syria two years ago, to be the most effective and dangerous of the armed rebel groups fighting the Assad regime. The front has repeatedly carried out complex operations against the regime, particularly suicide bombings.

It has secured considerably funding from the Persian Gulf monarchies because of its relatively moderate agenda, unlike the take-no-prisoners ethos of ISIL and the bloodthirsty Baghdadi.

Al-Nusra, led by a Syrian named Abu Mohammed al-Golani, also collaborates with other Islamist groups in the splintered Syrian opposition, often mounting joint operations.

These generally are aimed at the regime's forces, but in recent months they have been increasingly directed against ISIL as it sought to seize control of the northern front.

Despite his jihadist affiliation, Golani, although critical of the United States, has not threatened to mount attacks outside the Levant.

Al-Nusra moved against ISIL several weeks ago, joining non-Islamist and more moderate nationalist groups to drive it out of the front's home turf around the eastern oil city of Deir el-Zour, which ISIL had taken over in its drive to establish a jihadist "emirate" in Syria.

Suri returned to Syria sometime last fall, sent by Zawahiri to end the in-fighting and rally the jihadist groups under one banner. Al-Nusra and several rebel groups joined forces in January to push ISIL out of northern and eastern Syria.