For Islamic State, the 500-mile border between Syria and Turkey has been the main gateway for arms and foreign fighters entering its self-proclaimed caliphate.
Jihadis would fly to Istanbul, Turkey, then travel to remote hamlets in southern Turkey to be smuggled into Syria.
But that passageway has now been cut off by Syrian rebels and Turkish-backed Islamic factions that snatched a 54-mile strip of territory Sunday, Turkish officials and rebels said.
“The Turkish border with Syria was cleared Sunday of Daesh,” the Turkish state news agency Anadolu reported, using Islamic State’s Arabic acronym. The gains came 12 days after Turkey announced an offensive known as Operation Euphrates Shield.
The newly seized territory stretches between the cities of Jarabulus and Azaz in northwestern Syria and includes the Syrian border town of Rai, which for the last two years has flipped back and forth between Islamic State and rebel control.
The Turkish news agency reported that factions collectively known as the Free Syrian Army — a loose-knit group whose members say they espouse a secular non-Islamist vision for the country and have received Western support — now control a belt of land extending two to three miles inside the country.
One group, the Be Upright As You Were Commanded Brigades, posted a YouTube video showing its members storming positions near Rai.
But the effort also included the hard-line Islamist faction, Faylaq Al-Sham, which said on its official Twitter account Sunday that its fighters — shown earlier in photographs preparing for battle with Islamic State — were responsible for linking border territory west of Jarabulus with areas east of Rai.
Such collaboration speaks to the complexity of the conflict in Syria. Rebel groups have common enemies in Islamic State and the government of President Bashar Assad — which are also fighting each other — but different outside backers and long-term goals.
Turkey supports only some of the rebel factions. It is a sworn enemy of the Kurdish militia known as the People’s Protection Units, which it views as an ally of the Kurdish insurgents it is fighting at home.
But among the various factions fighting in Syria, the Kurdish militia is the most important U.S. ally against Islamic State.
The territorial gains follow other steps the Turkish government has taken to seal the border, including constructing a series of “modular walls.” Turkish crews continued building the first of these concrete barriers Saturday near Suruc, the state news agency reported.
Turkey says the walls are meant to stop all terrorists, including Kurdish rebels.
Bulos is a special correspondent.
5:40 p.m.: This story was updated with staff reporting.
This article was originally published at 10:15 a.m.