ISTANBUL (Reuters) - Islamic State militants in northern Syria are putting up "stiff resistance" to attacks by Turkish-backed rebel fighters, Turkey's military said on Wednesday, almost two months after it launched an incursion to drive them away from its border.

Supported by Turkish tanks and air strikes, the rebels have been pushing toward the Islamic State stronghold of Dabiq. Clashes and air strikes over the past 24 hours have killed 47 jihadists, the military said in a statement.

"Due to stiff resistance of the Daesh (Islamic State) terror group, progress could not be achieved in an attack launched to take four settlements," it said, naming the areas east of the town of Azaz as Kafrah, Suran, Ihtimalat and Duvaybik.

However, the operation to drive the jihadists away from the Turkish border, dubbed "Euphrates Shield", has allowed Turkish-backed rebels to take control of about 1,100 square km (425 square miles) of territory, the military said.

A Syrian rebel commander told Reuters the rebels were about 4 km (2.5 miles) from Dabiq. He said capturing Dabiq and the nearby town of Suran would spell the end of Islamic State's presence in the northern Aleppo countryside.

A planned major offensive on the Islamic State-held city of al-Bab, southeast of Dabiq and an important strategic target, depended on how quickly rebels could take control of the roughly 35 km (22 miles) in between the two cities, he said.

Al-Bab is also a strategic target for the Kurdish YPG militia, which, like the rebels, is battling Islamic State in northern Syria but is viewed as a hostile force by Turkey.

In a daily round-up on Euphrates Shield's 50th day, the Turkish army said 19 Islamic State fighters had been "neutralized" in clashes and eight rebels were killed. Twenty-two rebels were wounded and Turkish forces suffered no losses.

Turkish warplanes destroyed five buildings used by Islamic State fighters, while U.S.-led coalition jets "neutralized" 28 of the jihadists and destroyed three buildings, it said.

(Additional reporting by Tom Perry in Beirut; Writing by Daren Butler; Editing by Nick Tattersall and Louise Ireland)