Syrian children, refugees from the conflict in their homeland, sat beneath makeshift tents in Oncupinar, Turkey. Their faces poked out from behind torn pieces of scrap tarpaulin. Water boiled in pots above small fires. Men smoked cigarettes and women hand-washed clothing. In the distance, I heard the whump of, presumably, tank shells.

The distant blasts came from just over the Turkish-Syrian border. For much of the morning, fighters from the Islamic State in Iraq and Syria (ISIS) had been battling militias in the Kurdish village of Qustul Jendo near to the strategic Syrian town of Azaz, which ISIS took control of on September 18.

There would be nothing remarkable about this fight, if six major rebel factions hadn’t called on October 3 for “our brothers in ISIS to withdraw their troops and vehicles [from Azaz] to their main headquarters immediately.”

Instead, ISIS—an al Qaeda-affiliated militia that has become one of the strongest factions in the region—went on the offensive against the village of Qustul Jendo and opened up another front around Azaz. For the past two weeks ISIS and the Free Syrian Army-linked Northern Storm brigade have slugged it out for control of Azaz, and, more importantly, the Bab al-Salamah border crossing a few miles up the road.

Fighting broke out when ISIS attempted to kidnap a German doctor working at a local hospital on September 18. They took control of the town, as FSA reinforcements were sent from Aleppo to support the besieged Storm brigade’s fighters.

There was talk of a ceasefire, but that broke down. A member of Azaz’s media center, Hazem al-Azeze, attempting to broker the ceasefire, was shot in the neck by ISIS, bleeding out on a street, according to activist accounts.

In Syria, rifts between opposition factions have led to increased rebel-on-rebel violence.

“How can we fight Bashar al-Assad when we have a war with ISIS and the PKK [a militant Kurdish separatist group in Southeastern Turkey] at the same time?” said one opposition activist, fearful of reprisals. “We cannot focus on just Assad anymore, but have to always look over our shoulders at who is behind us.”

ISIS clashed recently with FSA brigades in the eastern city of Deir Ezzor and had reportedly declared war on the Farouk Brigades, a group falling under the FSA banner.

In northeastern Hasakah province, around the mixed Arab-Kurd town of Ras al-Ayn, sporadic fighting continues between the Islamist group Jabhat al-Nusra (JN)—headed by Abu Mohammed al-Joulani, an al Qaeda operative dispatched in late 2011 by ISIS’s leader, Abu Bakr al-Baghdadi, to establish a jihad group in Syria—and Kurdish militias, which have largely avoided being drawn into the conflict.

According to the London-based, pro-opposition Syrian Observatory for Human Rights, ISIS had attacked a JN base in Hasakeh Province, killing two Nusra militants while seizing weapons and equipment on September 22. It is also suspected of responsibility for a car bombing that killed seven on the Syrian side of the Bab al-Hawa border crossing into Turkey on September 17. It has additionally threatened a wave of attacks in the Turkish capital, Ankara, in reprisal of the Turkish government closing the border at Oncupinar, a key supply route for rebel groups.

Turkish Prime Minister Recep Tayyip Erdogan is facing acute domestic backlash for his government’s Syria policy: Turkey aggressively pursues regime change in Damascus, advocating direct Western military involvement in a conflict which has now killed around 115,000 people (of which 41 percents are estimated to be regime forces and allies) and laid waste to infrastructure while displacing around six million people.

The Turkish government, which initially sought to leverage a settlement between Damascus and its opposition, allows foreign fighters (scores of jihadists, referred to as al-Muhajirin, left Jabhat al-Nusra for ISIS earlier this year) and weapons to move freely across its territory, into Syria, and is widely believed to have moved weapons directly to Syrian insurgents—a charge which Ankara denies.

Many argue that the Turkish government uses both ISIS and JN as proxies.

Turkey’s policy of regime change has basically led to the dissolution of the Turkey-Syria border, now haunted by smugglers and fighters. Erdogan’s position has likely escalated the Syrian conflict and has removed any leverage Turkey may have had over the Syrian regime in negotiating a settlement.

It has also increased the likelihood of blowback from Damascus: a twin car-bombing in another Turkish frontier town, Reyhanli, in May brought carnage to a bustling market street, killing 52 people. That attack was linked by Ankara to a militant group tied to the Syrian regime. However, ISIS recently claimed responsibility for the attack—though its involvement seems unlikely.

Yet the Turkish parliament on Thursday voted to extend a mandate allowing it to send Turkish troops into Syria, claiming that Damascus’ chemical weapons—presently, the Organization for the Prohibition of Chemical Weapons (OPCW) has inspectors in Syria working to destroy the regime’s stockpile, following an attack in the Damascus suburb of Ghouta  late August—pose a threat to Turkey.

“We will continue to act with the reflexes of a great state,” Erdogan recently said, following Turkish fighter planes shooting down a Syrian helicopter that had strayed into the skies over Turkey last month, and an earlier deployment of additional Turkish troops to border regions. “I hope and believe that no one will misinterpret Turkey’s patience and restraint and attempt to test us.”

While ISIS and JN have emerged as among the most potent rebel factions, attracting a slew of recruits and taking the fight hard to the regime—a recent IHS Janes’ study reportedly estimated that around 50 percent of the 100,000-strong opposition is composed of hardline Islamists—the former appears to be angering many in the opposition repulsed by the group’s austere vision of an ultra-conservative Syria.

“They (ISIS) are fighting over what Islam is. They want everyone to be like them,” Ahmed, a refugee at the border said when the fighting in Azaz broke out two weeks ago. “They think that if you are not like them, they can kill you.”

Meanwhile, JN continues to gain support in rebel-occupied areas, by providing electricity, bread, and bus services to residents, according to the accounts of Aleppo activists.

Yet, ISIS does retain some degree of support. Speaking in the Turkish frontier town of Kilis late Friday, Abdallah, a fighter from the Islamist Ahrar al-Sham about to return to the frontlines after being patched up in a Turkish hospital for a wound sustained while fighting in Aleppo, said ISIS was ready to take the fight to the FSA.

“ISIS is strong and righteous,” he said clutching his hands together, a black prayer cap sat tight around his skull.