The Turkish military says three of its soldiers were accidentally killed and 11 others wounded by a Russian air strike in northern Syria.

The Kremlin said in a statement on February 9 that Russian President Vladimir Putin had expressed his condolences via phone to Turkish President Recep Tayyip Erdogan "in connection with the tragic incident" involving Turkish soldiers killed near the city of Al-Bab.

The soldiers were in a building that was hit by an air strike from a Russian warplane, a Turkish military statement said.

Russian Sputnik news agency reports that the Russian and Turkish presidents held a phone conversation earlier on Thursday.  Putin expressed condolences to Erdogan over the deaths of Turkish soldiers.  They also agreed to expand military coordination during the operation against militants from the Islamic State (IS) group and other extremist organizations in Syria. 

The Russian Defense Ministry said that along with stepping up cooperation in conducting military operations in Syria, the two countries would also share information.

Chief of the Russian General Staff General Valery Gerasimov held telephone talks with his Turkish counterpart, during which the issues of the fight against international terrorist groups in Syria and the situation in the northeast of the province of Aleppo were discussed, according to Sputnik.

“The heads of the General Staff agreed to a closer coordination of the joint actions and to exchange information about the situation on the ground," a statement released by the Russian Ministry of Defense said.

Financial Times reports that the Turkish military said both Ankara and Moscow were investigating the Russian air strike. A Turkish official said that it was not expected to harm relations between the two countries, citing how ties were not damaged when a Turkish police officer shot and killed Russia’s ambassador in December.

Russia supports troops loyal to Syrian President Bashar al-Assad who are battling IS militants and other armed groups who want to oust Assad.

Turkey is also fighting extremist Islamic groups in Syria but supports the moderate opposition groups trying to overthrow the Syrian government.

Reuters reports that U.S. Vice President Mike Pence also expressed condolences for the Turkish casualties in a call with Turkish Prime Minister Binali Yildirim, in which they discussed cooperation in the fight against terrorism.

Turkish-backed Syrian rebels pursued a major offensive against the IS-held Syrian city of al-Bab, 30 kilometers south of the border with Turkey.

Al-Bab is a major economic hub for the militants and lies on a key crossroads for the region north of Aleppo.  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, Reuters said, noting that Turkey 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.