Turkish tanks and members of the Free Syrian Army took part in an operation to regain control of the border city of Jarabulus. (Sedat Suna/European Pressphoto Agency)

Pentagon officials said that U.S.-trained Syrian forces helped recapture a strategic border town on Wednesday, highlighting the role of local fighters who received American support in an earlier, ill-fated effort to build up an army against the Islamic State.

The operation in Jarabulus, perched along Syria’s border with Turkey, was a rare high-profile operation involving fighters who went through the short-lived U.S. train-and-equip program, which was supposed to be the Pentagon’s main vehicle for combating the Islamic State in Syria but instead became a symbol of its failure to navigate the complexities there.

U.S. officials said the Syrian forces, which they call the “vetted Syrian opposition,” made up at least part of the hundreds of Syrian fighters who, along with Turkish troops, easily retook Jarabulus on Wednesday. It’s unclear exactly what role the Syrian fighters played in the lightning-fast battle, which was launched from the Turkish side of the border and included Turkish troops, tanks and planes. American A-10 and F-16 aircraft also conducted airstrikes.

The Islamic State’s defeat in Jarabulus deprives the militant group of its last major town along Syria’s border with Turkey, which has been its primary route for securing reinforcements and supplies.

The operation marked the Turkish military’s first incursion in Syria’s long war. It was also a shift for the United States, which in recent months has primarily focused its support on other Syrian rebels: a mix of Kurdish and Arab fighters fighting under the banner of the “Syrian Democratic Forces.” Earlier this month, with the backing of U.S. Special Operations forces, SDF fighters retook the city of Manbij, to the south of Jarabulus.

But the U.S.-backed Syrians in Jarabulus, unlike the SDF, have undergone extensive vetting by American officials and received training from U.S. military personnel in Turkey as part of the earlier effort, which sought to create an anti-Islamic-State force from scratch.

The program, launched in 2015, was plagued with problems from the start. Many Syrians were unable to make it through the vetting process, or quit to rejoin their families. When members of an initial group returned to Syria that fall, they were attacked by rival forces, and some turned over weapons to al-Qaeda-linked fighters. Under pressure, Pentagon officials then decided to overhaul the program, focusing instead on creating looser partnerships with military units already in Syria.

One defense official, who spoke on condition of anonymity to discuss operations in Syria, said forces from the vetted group had been conducting operations just south of the Turkish border for months. “They’ve done a lot of it with Turkish support,” the official said. He said the Pentagon has continued its support for those forces even after the training program was revamped.

According to a senior U.S. official, U.S. and Turkish authorities recruited Syrian fighters from northwest Syria ahead of the Jarabulus operation, brought them into Turkey and then transported them to the area opposite the Syrian city. The United States provided aerial surveillance for the operations and stationed Special Operations forces on the Turkish side of the border.

Karen DeYoung in Ankara contributed to this report.