Three Turkish soldiers were killed and four wounded on Tuesday in a rocket attack by Islamic State (IS) militants in northern Syria, in the first deadly attack on Ankara's armed forces to be blamed on the jihadists in Turkey's cross-border incursion.

Turkey launched an unprecedented operation inside Syria on August 24. Dubbed Euphrates Shield, it backs pro-Ankara opposition fighters in the goal of rooting out IS jihadists and Kurdish militia from the border area.

A senior Turkish official said two soldiers were killed on the spot and five injured in the attack by IS.

One of the wounded soldiers later died in hospital despite all attempts to save his life, lifting the death toll to three, an army statement quoted by NTV television said.

The fatalities are the first of the Turkish operation inside Syria to be blamed on IS and Ankara's biggest single loss of life in the offensive to date.

Turkey had blamed the death of one soldier on August 28 in a similar attack on Kurdish militia.

The army said in the statement carried by NTV television that the deaths came in a rocket attack on two Turkish tanks.

The army said the attack took place in the village of Wuquf south of Al-Rai, where Turkish tanks opened a second front in their Syria operation at the weekend.

The area is west of Jarabulus near the Turkish border which was retaken by pro-Ankara rebels at the start of the operation from jihadists.

Turkish television showed pictures of military helicopters flying across the border to take the wounded for treatment in Turkey.

Separately, two pro-Ankara Syrian fighters were killed and two others wounded in clashes in the same region, the army statement added.

- 'IS cleared from border' -

Turkey has so far hailed its operation as a success and IS jihadists were at the weekend expelled from their last positions along the Turkish-Syrian border, depriving the group of a key transit point for recruits and supplies.

Turkey wants to establish a safe zone in the 98-kilometre (61-mile) area stretching from Jarabulus to Azaz to the west. The government says this has been completely secured in the weekend's operation.

The army also said on Tuesday "44 targets were struck 153 times with precision by Firtina howitzers in a region identified as belonging to terrorists," adding that coalition warplanes also launched air raids on IS positions.

Syrian rebels, backed by coalition forces, retook two villages near Al-Rai, it added. "The operation is continuing in the region."

Until now there had been few reports of clashes between Turkey or its allied fighters with IS. But there had been indications of intense fighting with the Kurdish Peoples' Protection Units (YPG) militia.

The YPG is a key partner of the US-led coalition against IS, and has recaptured large swathes of territory in Syria from the extremist group.

But NATO member Turkey, an active participant of the anti-IS coalition, considers the YPG a "terrorist" group and has been alarmed by its expansion along the border, fearing the creation of a contiguous, semi-autonomous Kurdish region in northern Syria.

The Turkish presidency said earlier it hoped for a truce in northern Syria between opposition fighters and the regime of President Bashar al-Assad in a week, after talks between President Recep Tayyip Erdogan and world leaders at the G20 in China.

Erdogan's spokesman, Ibrahim Kalin, revealed that the Turkish leader had met separately a second time with Russian and US counterparts Vladimir Putin and Barack Obama before leaving the G20 meeting in Hangzhou.

Turkey and Russia have been on opposite sides of Syria's five-and-a-half-year civil war, with Moscow backing Assad and Ankara supporting the opposition against him.

However, there have been signs of a rapprochement, with Kalin saying Putin had told Erdogan he fully supported the Turkish operation.