A Turkish soldier was killed Wednesday in a car bomb attack in northern Syria where troops are helping Syrian rebels capture a key town from Islamic State jihadists, the army said.

The attack took place near the town of Al Bab, 25 kilometres (15 miles) from the Turkish border, which has become a key target of the army's more-than-three-month campaign inside Syria, the army said in a statement quoted by the state-run Anadolu news agency.

Six soldiers were wounded, one of them seriously, it added. An earlier reported toll had said two soldiers were killed.

The Turkish army has pressed ahead with an ambitious campaign inside Syria to back opposition fighters who have since August captured Jarabulus, Al Rai and the symbolically important town of Dabiq from IS.

However, capturing Al Bab -- where the jihadists reportedly regrouped after fleeing an earlier offensive -- has proved much tougher in an operation that has already taken several weeks.

After the lightning speed of the earlier campaign, the Turkish army has suffered increasing casualties in the fight for Al Bab, with most the deaths blamed on IS attacks.

In November, however, four Turkish soldiers were killed by an air strike the army said it believed was carried out by President Bashar al-Assad's forces.

Meanwhile, the army said on November 29 that two Turkish soldiers had gone missing in Syria, the first time such an incident had been reported in the campaign.

The IS-linked Amaq news agency claimed that the jihadist group had taken the pair hostage.

The Turkish government says its military offensive is seeking to cleanse its border from IS and Syrian Kurdish militia forces, regarded as terror group by Ankara.

Turkey has for years been pressing for a safe zone inside Syria to shelter refugees along its border, but so far, its calls have not been heeded.

Turkish media said that after the deadly attack, the air force struck IS facilities inside Syria, destroying 12 targets and killing 23 extremists. It is not possible to verify the toll.