BOTH Syrian revolutionary and black Islamic flags now flutter in Idleb, the largely rebel-held province in north-western Syria, close to the Turkish border. But the red flags flying atop the town hall in Tel al-Karama, in the north of the province, and the checkpoint outside it (pictured) signal not a fight against President Bashar Assad but a score to settle with another rebel group. Tel al-Karama is the hometown of Firas al-Abseh, known as Abu Muhammad, a Syrian Islamic extremist killed last week by fighters of the Farouq al-Shamal Brigade, which is part of a large rebel group based in Homs province. Abu Muhammad led the Mujahadeen Shuraa Council, a team of 100 Syrians and foreigners, inspired by al-Qaeda, which kidnapped two journalists in late July, a Brit and a Dutch national, threatening to kill them before they were rescued.

Initially rebels had welcomed Abu Muhammad, a bald, staid-looking dentist who had come to set up a medical camp, even giving him weapons, says Abu Azzam, a Farouq leader based at the Bab al-Hawa border crossing from Turkey into north-western Syria. But Farouq and other groups in the area had grown increasingly uneasy about his behaviour. He refused to join battles with Muslims he deemed too liberal and gathered foreign jihadi friends, from Britain, Libya and Pakistan, in a tented camp close to the border—a number of them man a hut at the border where tense conversations were being had with Farouq fighters. “He saw himself as an emir and wanted to control everything,” says Abu Ali, another Farouq member. “He was another Assad, just an Islamist version.”

Most fighters disagree with killing fellow rebels, but seem pleased that Farouq, whose own ideology is moderately Islamist, took action. “We don’t want foreigners or extremists here because this is our fight and Syrians are moderate,” says one who leads a small independent group of rebels out of a village in the area.

The demise of Abu Muhammad offers a window into the local dynamics of Syria’s bloody conflict and the tensions between the different groups of fighters. Although they often work together, competition for money, weapons and influence has been growing, and religious faultlines are deepening. Jihadists make up less than 10% of Syria’s opposition fighters, according to a study by the Quilliam Foundation, a counter-terrorism think tank based in London, but their numbers are rising. More worrying to many rebel leaders is that the country is becoming a magnet for foreign fighters who have been seen across the provinces of Idleb and Aleppo.

Abu Muhammad was well known in jihadist circles. He was born in Saudi Arabia to Syrian parents, and studied medicine at Aleppo university before moving back to Saudi Arabia. He was imprisoned there and in Sudan for sending fighters to Afghanistan and had once met Abu Musab al-Zarqawi, the Jordanian militant who led al-Qaeda in Iraq. When the revolution started in Syria he came running back. Having helped wrestle control of the Bab al-Hawa border post from the regime’s forces in July, he moved in and staked out his territory, raising the banner associated with al-Qaeda, a black flag marked by a white stamp and the Muslim declaration of faith. Some fighters said he planned to implement strict Islamic rules, including stopping women without headscarves from crossing the border and banning smokers.

It was then that other local leaders near the Baba al-Hawa border crossing say they agreed Abu Muhammad had to be dealt with. Fighters say they killed him by a single gunshot and returned to his family with a delegation to explain the matter. “This isn’t about a fight between different rebel groups,” insists Abu Azzam, the Farouq leader. “We don’t want chaos and people imposing anything on us.”

But the red flag, which Tel al-Karama’s residents said was a signal of blood, suggests Abu Muhammad’s men want revenge. Some of them are calling for the killers to be handed over. “He was a good man and Farouq just want the border so they can tax people and make money,” says a friend of Abu Mohammed who lives in southern Turkey. (So far there is no sign of any money being taken at the border.) “It is not right.” On spying the red flag fluttering at the checkpoint manned by men from Mujahadeen Shuraa Council, Farouq rebels turn back and take a different road. And there remains the small matter of Abu Muhammad's men. The al-Qaeda flag still flies above their small hut at the border post at Bab al-Hawa, suggesting that visitors of all hues are welcome in Syria.

Correction: This article initially stated that Abu Muhammad was doctor. In fact he was a dentist. This was corrected on September 14th.