GAZIANTEP, Turkey — Shortly before its operatives killed 14 Iraqi Shi’ite children in a school bombing this month, the group once known as Al Qaeda in Iraq sent guerrillas into northern Syrian villages with orders to reopen local Sunni classrooms.
In a series of early fall visits, the militants handed out religious textbooks along with backpacks bearing the group’s new name: the Islamic State of Iraq and Syria.
A four-hour drive to the east, a rival Al Qaeda faction called Jabhat al-Nusra was busy setting up a jobs program in Ash-Shaddadi, a desert town it has held since February.
The Islamists restarted production in an oil field that had been idled by fighting, and fired up a town’s natural gas plant, now a source of income for the town and its new rulers.
The two rebel groups, with their distinct lineages to the terrorist network founded by Osama bin Laden, have concentrated Western fears of rising jihadist influences within Syria’s rebel movement. Two and a half years after the start of the country’s uprising, Islamists are carving out fiefdoms.
‘‘We all have the same aqidah [Islamic creed] as al-Nusra or the Islamic State,’’ said a 23-year-old Jordanian Palestinian who gave the name Abu Abdallah in an interview in Jordan and who fights for rebels allied with the Islamists. ‘‘The aim is to free the Muslim lands and have the Islamic flag there.’’
The prominence of the two groups — as fighters, as recruiters, and, more recently, as local administrators — appears to have accelerated even as the US administration seeks to boost moderate and secularist rebels with new arms and training.
Multiple independent studies as well as Western and Middle Eastern intelligence officials show the hard-line Islamists surging ahead by almost every measure, undermining Western efforts to find a democratic alternative to Syrian President Bashar Assad.
The Al Qaeda affiliates have clashed with other rebels, and occasionally with each other, and their heavy use of foreign fighters and attempts to impose an ultraconservative ideology have alienated some Syrianse.
‘‘The situation is so bad,’’ said Mohammed Abdelaziz, an activist in the city of Raqqa who said the Islamic State of Iraq and Syria — known as ISIS — criminalized tobacco use and carried out public executions. ‘‘A lot of people have just escaped the city.’’
But other Syrians have embraced the jihadists and welcomed the return of order in towns hit by months of war. A Syrian fighter who called himself Abu Bahri said about 100 people from his town of Azaz joined ISIS after becoming frustrated with the inefficiency of the moderate brigade, which was in charge of the town.
US and Mideast officials say the two Qaeda groups are a magnet for much of the foreign cash and most of the foreign fighters streaming into Syria.