Turkish-backed rebels launched an assault on city of al-Bab in northern Syria held by the Islamic State (IS) militants on Friday, opposition fighters said, and Turkish warplanes hit dozens of Islamist militants targets in support of the offensive.
Hundreds of Arab and Turkmen fighters involved in the assault took control of at least two villages west of al-Bab, the fighters said. Turkish state media said late on Thursday that Ankara had sent 300 Turkish commandos to northern Syria as a reinforcement.
The operations are the latest in Turkey's "Operation Euphrates Shield", a military incursion launched three and a half months ago in support of the rebels, and meant to push both IS militants and Kurdish fighters back from the border.
The Turkish army said its air strikes on Friday morning destroyed 34 IS targets, including militant bases, shelters, vehicles mounted with guns, and ammunition depots. Ten targets had also been hit the day before.
The military also said the rebels it backs had seized control of an important highway between the towns of al-Bab and Manbij, around 50 km (30 miles) to the east.
"There is a major assault under way," a fighter with the Turkmen Sultan Murad brigade speaking from inside Syria said. "God willing we will break (IS) resistance this time. Very powerful troops were sent last night."
The Syrian Observatory for Human Rights, which monitors the conflict through a network of sources in the country, confirmed there was an increase in the number of Turkish troops with the Euphrates Shield forces and that they were shelling heavily on Friday as they attempted to advance on al-Bab.
The Observatory said explosions triggered by IS had caused casualties in a village close to al-Bab. It also said it had received information that 12 civilians were killed and 10 wounded as a result of air strikes and bombardment by Turkish forces targeting al-Bab.
The advance of the Turkish-backed forces potentially pits them against both Kurdish fighters and Syrian government forces in an increasingly messy battlefield.
Al-Bab is of particular strategic importance to Turkey, partly because Kurdish-dominated militias have also been pursuing a campaign to seize it.
Ankara is determined to prevent the Kurdish YPG militia, which it sees as a hostile force, from joining up cantons it controls along the Turkish border, for fear that would stoke Kurdish separatism at home.