Al Qaeda-linked fighters have struck back at a loose alliance of Syrian insurgents, including Islamists and other jihadists, retaking territory it had either ceded or was forced from and attacking foes with suicide bombings—the latest coming on Monday night, when eight Syrian rebels were killed in an attack on a checkpoint near Idlib city in northern Syria.

The counteroffensive by the Islamic State of Iraq and Sham (ISIS), in a war within the wider war to topple President Bashar al-Assad, has confounded many analysts. Some eExperts had predicted that, with the array of different brigades challenging the jihadist group—from Western-backed moderates to hard-line Islamists—it would only be a matter of time before ISIS, which has also launched a successful offensive on the Iraqi city of Fallujah, would be routed or at least severely diminished.

Fighting between ISIS and other Syrian insurgents erupted nearly two weeks ago and has left at lest 700 dead, according to the Syrian Observatory for Human Rights, a UK-headquartered anti-Assad monitoring group that relies for its information on a network of Syria-based activists.

According to the Syrian Observatory the suicide bombing of the rebel checkpoint in Idlib province caused a massive explosion. “Eight fighters from Islamist and other rebel brigades died after a huge bombing carried out by ISIS fighters,” the Observatory said.

With no let-up in the internecine fighting and clashes in some areas seeing ISIS battling jihadists from another, smaller al-Qaeda affiliate, Jabhat al-Nusra, al-Qaeda’s point man in Syria, Abu Khalid al-Suri, has urged the opposing sides to reach an accord.

The Aleppo-born al-Suri called on al-Qaeda’s leader, Ayman al-Zawahiri, who appointed him as envoy in Syria, to intervene and, in an audio recording posted online, advised him to “cut a patient so as not to damage the whole body, my sheikh.”

ISIS, which has provoked widespread resentment in insurgent ranks for imposing draconian Islamic rules on towns it controls and assassinating rival rebel leaders, also released a new defiant online audio message this weekyesterday saying the group is the “salt of this earth and crown of our heads and the head of the shaft of the nation in the face of the enemies of the religion.”

Led by the ambitious Abu Bakr al-Baghdadi, who envisages carving out his own caliphate stretching across the Levant, ISIS claims those opposing it are involved in a “dirty task” serving the interests of the West and acting like the Iraqi Sunni Sheikhs who, with U.S. backing, formed the 2005 Anbar Awakening and curtailed al-Qaeda in Iraq.

ISIS opponents accuse al-Baghdadi and his men—he is believed to be able to field more than 10,000 fighters—of assisting Assad by, at a minimum, distracting the insurgency against the Syrian President and at worst colluding with the regime.

The infighting has prompted hand-wringing by jihad scholars, who have also been firing off online contributions to a raging debate on jihadist forums over the rights and wrongs of the conflict. A key Islamist brigade opposed to ISIS, Ahrar al-Sham, has close ties with core al-Qaeda.

The ISIS pushback in the past this weektwo days has seen the group retake the town of Al Bab to the northeast of Aleppo, according to opposition activists there, and the jihadists were expected to return to districts in Aleppo they had fled from just days ago. The northeastern city of Raqqa is reportedly back in ISIS’s control following a decision by Islamists battling al-Baghdadi’s fighters to agree a truce—but it was unclear how long that may hold after accusations that ISIS had executed foes, burying them in a mass grave. The Syrian Observatory reported fighting had resumed. ISIS was still on the back-foot in Jarabulus, near the Turkish border, where fierce fighting was reported yesterday.

Despite the ISIS fight-back, al-Baghdadi is drawing criticism from important figures within al-Qaeda. “I think he is in big trouble with the broader al-Qaeda network,” says Thomas Joscelyn, a jihadist watcher for the Washington DC think tank The Foundation for the Defense of Democracies. “Al-Baghdadi has important supporters but I think more chips are against him.”

Aron Lund, an analyst with the Washington, D.C.-based think tank Carnegie Endowment for International Peace, argues that the push behind the dizzying series of Islamist mergers and coalition-forming in opposition to ISIS came from “a wave of encouragement and pressure from foreign funders such as Saudi Arabia, Qatar and various private Kuwaiti Islamist sponsors.”

Turkey, which has been accused in the past of allowing jihadists to cross the border with Syria with little obstruction and even of supplying them with with arms, has also weighed in to help groups fighting ISIS. YesterdayYesterday, Turkish police raided the offices of the charity Humanitarian Relief Foundation in the southern Turkish town of Kilis amid accusations it has ties with jihadists. Police also launched counterterrorism raids in Istanbul and half-a-dozen other cities, detaining at least two senior al-Qaeda suspects, according to the Dogan news agency.

UN officials warned that the infighting across northern Syria areas controlled by the rebels had forced them to postpone their polio vaccination campaign launched after more than a dozen cases of the disease were reported in the war-torn country.

With the rebels turning their guns on each other, Syrian government forces appeared to have made inroads in an unfolding offensive on Aleppo, Syrian’s onetime commercial hub, which has been divided between government forces and rebels for more than a year. After a long stalemate in which little territory changed hands, rebels have been pressed on the eastern approaches to the city after Assad forces retook a handful of strategic outlying towns in the weeks leading up to Christmas.

And the government has maintained its aerial attack—mainly involving helicopters dropping so-called barrel bombs filled with high explosive and fuel. Human-rights groups have condemned the Syrian air force’s use of barrel bombs, arguing that as an indiscriminate weapon they breach international laws of war.

Now activists with the Aleppo Media Center, say government forces have retaken part of Sheikh Najjar, an important onetime industrial neighborhood five miles to the north of Aleppo. If regime forces are able to recapture the whole district, rebel supply lines from Aleppo to Turkey could be cut and “the whole liberated area of Aleppo would be isolated and besieged,” the Media Center said in a statement.

The government offensive on Aleppo is part of an apparent effort to change the balance of military power—what analysts like to call the “facts on the ground”—ahead of the slated Geneva 2 peace talks being pushed by the U.S. and Russia.

Syrian government spokesmen have become sharper in their tone in the diplomatic lead up to the talks that are meant to commence next week and yesterday (Jan 13) Assad’s foreign ministry sneered at pre-talks in Paris between Russian and U.S. diplomats exploring ways to engineer a ceasefire ahead of the Geneva gathering and to organize aid to civilians. In a statement the foreign ministry ridiculed the participants, saying they were “detached from reality.”