By Suleiman Al-Khalidi and Daren Butler
AMMAN/ANKARA (Reuters) - Russian air strikes accidentally killed three Turkish soldiers during an operation against Islamic State in Syria on Thursday, the Turkish military said, highlighting the risk of unintended clashes between the numerous outside powers in a complex war.
"During an operation by a Russia Federation warplane against Islamic State targets in the region of the Euphrates Shield operation in Syria, a bomb accidentally hit a building used by Turkish Army units," the Turkish military said in a statement. Eleven other soldiers were wounded.
The Kremlin said Russian President Vladimir Putin had called Turkish counterpart Tayyip Erdogan and expressed his condolences, blaming the incident on poor coordination between Moscow and Ankara.
Besides Russia and Turkey, the foreign powers embroiled in Syria's increasingly convoluted six-year-old war include Lebanon's Hezbollah and other Iranian-backed militias, and members of a U.S.-led coalition fighting Islamic State.
Russia is a key ally of Syrian President Bashar al-Assad, while Turkey supports the rebels opposing him. In 2015, Turkey shot down a Russian air force jet that it said had crossed into Turkish airspace, though Moscow denied that happened.
The two countries have since repaired relations, and Thursday's Kremlin statement said the two leaders had agreed to step up military coordination against Islamic State.
U.S. Vice President Mike Pence expressed condolences for the Turkish losses in a call with Turkish Prime Minister Binali Yildirim, in which they discussed cooperation in the fight against terrorism, Yildirim's office said.
CLOSING IN ON AL-BAB
Turkish-backed Syrian rebels meanwhile pursued a major offensive against the IS-held Syrian city of al-Bab, 30 km (20 miles) south of the border with Turkey. Their advances risk putting them in conflict with Syrian government forces also closing in on the city from the south.
A rebel commander said fighters of the Free Syrian Army (FSA), working with Turkish commanders, were moving forward from territory near the western gates of al-Bab, which they had stormed on Wednesday.
"The battles began a short while ago to complete what had been achieved yesterday," said a commander of a leading FSA group fighting in al-Bab, who requested anonymity.
The capture of the town would deepen Turkey's influence in an area of northern Syria where it has created a de facto buffer zone. It launched its Euphrates Shield operation in August, backing Syrian rebels with special forces, tanks and aircraft to sweep Islamic State from its border area and stop the advance of a Kurdish militia.
Al-Bab is a major economic hub for the militants and lies on a key crossroads for the region north of Aleppo. Syria's army secured a string of villages on the southern edge of the city on Thursday, state media said.
The Turkish military said it had killed 44 militants in aerial and artillery strikes and clashes in northern Syria. Five Turkish soldiers were killed in the clashes, the private Turkish news agency Dogan said.
(Reporting by Suleiman Al-Khalidi and Ece Toksabay; Additional reporting by Daren Butler in Istanbul and Andrey Ostroukh in Moscow; Editing by Mark Trevelyan/Nick Tattersall)