Turkey and its rebel allies opened up a new line of attack in northern Syria on Saturday as Turkish tanks crossed the frontier from Kilis province, making a western thrust in an operation to sweep militants from its border.

The private Dogan news agency reported at least 20 tanks and five armored personnel carriers crossed at the Turkish border town of Elbeyli, across from the Syrian town of al-Rai. The new incursion is unfolding about 55 kilometers (34 miles) west of Jarablus, where Turkish forces first crossed into Syria ten days ago.

Open gallery view Map showing Turkey's second incursion into Syria in al-Rai.

The tanks entered from the Turkish border village of Elbeyli and linked up with Turkish-backed Syrian rebels at al-Rai, who are participating in the operation, dubbed Euphrates Shield.

The official Anadolu News Agency said that "with this new phase of the operation, the Azaz-Jarablus line is expected to be cleared of terror elements."

Turkish-backed Syrian rebels meanwhile said they had captured three more villages to the west of Jarablus from the Islamic State group, bringing them to 21 kilometers (13 miles) from those positioned at al-Rai. The gap is the last remaining stretch of the Syrian border under ISIS control.

The incursion came a day after Turkey renewed its airstrikes in Syria. On Saturday, a senior U.S. diplomat said that U.S. forces hit Islamic State targets overnight near Turkey's border with Syria using a newly deployed mobile rocket system, HIMARS, or "High Mobility Artillery Rocket System". It was not immediately clear when the system was deployed at Turkey's border.

Turkey renewed air strikes on ISIS sites in Syria on Friday, extending operations along a 90-km (56-mile) corridor near the Turkish border which Ankara says it is clearing of jihadists and protecting from Kurdish militia expansion.

Turkey's 10-day-old offensive, its first major incursion into Syria since the war started five years ago, has alarmed the West.

Open gallery view The High Mobility Artillery Rocket System (HIMARS) fires the Army's new guided Multiple Launch Rocket System during testing at White Sands Missile Range. Credit: Wikicommons

Turkey's military says its right to self-defense as well as UN resolutions to combat the ISIS group justify its Syria incursions.

Turkey and allied Syrian rebels have also fought U.S.-backed Kurdish forces known as the People's Protection Units, or YPG, around Jarablus. Turkey views the YPG as an extension of the Kurdistan Workers' Party, or the PKK, which Turkey and its allies consider a terrorist organization.

The U.S. has provided extensive aid and airstrikes to the YPG-led Syria Democratic Forces, which have proven to be highly effective against ISIS. The Syria Democratic Forces, which also includes Arab fighters, has taking a large swath of territory from the extremists along the border with Turkey and closed in on Raqqa, the de facto capital of the extremist group's self-styled caliphate.