BEIRUT - A rift between Syrian jihadis and their fellow fighters from al-Qaida's Iraqi wing may lead to internecine war among some of the most effective rebel groups in combatting President Bashar Assad.Trouble has been brewing since April over what Syria's Nusra Front regards as a power grab by Abu Bakr al-Baghdadi, leader of the Islamic State of Iraq. Now, Baghdadi's insistence that he will keep fighting as head of a united jihadi brigade in Syria, defying orders from al-Qaida chief Ayman Zawahri, has brought the two groups close to turning on each other.PUSHING BAGHDADI OUTA source close to Nusra leader Abu Mohammad Golani described Baghdadi's defiance as dangerous. "We have no choice but to confront them, or Zawahri himself has to deal with these people," he said.Nusra was ready to fight Baghdadi's forces and kick them out of Syria, but "Golani does not want bloodshed among brothers in Islam, he added. "Right now there is a decision to avoid them... but if he acts in a way that goes against Syria's interest he will be pushed out by force, him and his people."Beneath the bluster, Nusra fighters appear to be in no position for now to challenge Baghdadi's forces, and would need time to regroup and find allies among Syria's other rebels.A senior commander from a hardline Islamist rebel brigade in the northern province of Idlib said Baghdadi's men would probably win a direct clash."Nusra was weakened by (Baghdadi's) takeover and weakened even more by the split that happened," he said. "It will be very difficult for Golani or anybody to bring it back from ashes."With powerful, mostly foreign, fighters on his side, Baghdadi forced Golani and some of his men to go underground, confiscating some Nusra weapons. Many other Nusra fighters went home or joined other Islamist brigades.But the source close to Golani said the fact that most of Baghdadi's fighters were non-Syrians meant they could end up isolated, even among the jihadis, because they were more concerned with imposing an Islamist agenda than toppling Assad.Resentment about Baghdadi's agenda in Syria echoes the way that al-Qaida fighters alienated many Sunni fighters during the Iraqi insurgency against the U.S. occupation forces and the Shi'ite-led government in Baghdad. This could encourage other rebel brigades to join a Nusra backlash against Baghdadi."Baghdadi and those who believe in his extreme thinking, they are mostly foreigners and they are on their own," the source said. "Nusra is back to work," he added, saying Golani had ordered his commanders to prepare to resume operations.Despite losing ground to Baghdadi's men in the north, particularly in Aleppo and Raqqa provinces, rebels say the Nusra Front remains active and prominent in operations in the southern province of Deraa, near the border with Jordan.Any resurgence of the Nusra Front, which fights alongside other rebel brigades against Syrian government forces, would further complicate Western efforts to support Assad's opponents.The United States has been reluctant to arm the rebels because of fears that weapons could end up in the hands of anti-Western jihadis such as the Nusra fighters. However, after a string of Assad gains around Damascus and near the Lebanese border, backed by Lebanon's Shi'ite militia Hezbollah, President Barack Obama said Washington would increase military aid.ARMING A FRACTURED FORCEAny weapons which are sent would flow into a fractured rebel force. "Nusra believe, and they are right, that this is their land, it is their Syria and they have the right to lead the battle here," said the senior rebel commander in Damascus.Islamist sources close to al-Qaida's thinking say that Baghdadi's attempt to merge the Iraq and Syrian wings of the movement did not contradict Zawahri's belief in a hierarchy and structure that could form the basis of a powerful Islamic state.Unlike bin Laden, who believed al-Qaida should train fighters to carry out attacks across the globe, possibly autonomously, Zawahri wanted a more rigid command structure.Baghdadi's failure to consult over the merger and Golani's popularity among Islamist rebels, in contrast to the way al-Qaida alienated itself in Iraq, made it unacceptable."Golani is the son of Syria and he was so far doing a great job in paving the way for the creation of the (Islamic) state as a choice of people not by force, so Baghdadi in a way is an obstacle," the source said."Tension is increasing, it is about to reach boiling point. Both sides are saying they are right. A clash between them could occur soon and if it happens, it will be ugly," said a senior rebel commander in Damascus who is following the dispute.The two-year uprising against Assad has drawn fighters from many foreign countries to both sides, in what is increasingly a sectarian struggle between the main denominations of Islam. Some Iraqi Shi'ites are fighting for Assad, whose Alawite sect is an offshoot of Shia Islam, while Iraqi Sunni radicals who once took on US-led forces at home have joined the Syrian rebels.Baghdadi's attempt to unite the Syrian and Iraqi wings of al-Qaida has provoked the dispute at a sensitive time when some Western governments are considering arming more moderate rebels, but fear the weapons might fall into the radicals' hands.In April Baghdadi announced his Islamic State of Iraq was merging with the Nusra Front, which has staged some of the deadliest attacks on Assad's forces.This apparently unilateral move opened up bitter and public rifts with the Nusra Front leadership - which resisted what it saw as his bid for overall power - and with Zawahri, the global al-Qaida leader who instructed him to put the merger on hold in an apparent attempt to settle the row.Baghdadi dismissed the demand from Zawahri, who has headed al-Qaida since U.S. forces killed Osama bin Laden in 2011. The merged Islamic state of Iraq and Levant "is staying as long as we have a pulse and an eye that blinks... We will not compromise over its existence," Baghdadi responded earlier this month."After consultation I decided to (follow) the order from God over the order that opposes it," he added in an audio message.Nusra fighters, other rebels and Islamic sources reacted by saying Baghdadi had effectively severed his al-Qaida links."He rejected the ruling of Sheikh Zawahri and therefore he is no longer a brother of al- Qaida," said a senior Nusra commander. "After Sheikh Zawahri ruled in our favour, the State (Islamic State of Iraq and Levant) is illegitimate."