ISTANBUL (Reuters) - A Turkish soldier was killed and two others wounded in a bomb attack by Islamic State militants near the northern Syrian city of al-Bab, Turkish security sources said on Sunday.

The three soldiers were evacuated alive by helicopter on Saturday and taken to the southern Turkish town of Gaziantep, but one of them died from his injuries, the sources said.

Turkey launched an incursion into Syria in August, sending in warplanes, tanks and special forces in support of largely Turkmen and Arab rebels, to try to drive Islamic State and Kurdish militants away from its border.

Turkish President Tayyip Erdogan said last week that Turkish-backed forces were just 2 km (1.25 miles) from Islamic State-held al-Bab and were expected to take it quickly despite some resistance.

Al-Bab is of particular strategic importance to Turkey because Kurdish-dominated militias have also been pushing to seize it. Ankara is determined to prevent Kurdish forces from joining up cantons they control along the Turkish border, for fear it will stoke Kurdish separatism at home.

Although Turkey is a NATO member and part of the U.S.-led coalition against Islamic State, Washington has said it is not providing support for the Turkish bid to take al-Bab.

The U.S. has provided military support to Kurdish militia fighters in northern Syria which Ankara views as a hostile force.

(Writing by Nick Tattersall; Editing by Keith Weir)