Turkey bolstered its ground forces in northern Syria in a possible lead-up to renewed battles between the Turkish military and local Kurdish forces, a monitoring group and a Syrian opposition commander said Wednesday.

According to the Britain-based Syrian Observatory for Human Rights, which tracks the civil war through a network of activists on the ground, Ankara deployed a column of armored vehicles to the Syrian towns of Azaz and Marea.

The towns, held by Turkey-backed Syrian opposition fighters, are on the front lines with rival, U.S.-backed Syrian Kurdish forces.

Turkey, which first sent ground forces into Syria last year, perceives the Syrian Kurdish fighters as an extension of its Kurdish insurgents who have waged a three decade-long insurgency against Ankara. Syrian opposition forces, for their part, accuse the Syrian Kurdish fighters of colluding with pro-government forces to defeat them.

The Observatory said preparations were underway for a joint Turkish-Syrian opposition campaign to seize towns from Kurdish control in the area.

A commander in a Turkey-backed opposition faction said that an unusually large contingent of Turkish forces had entered northern Syria on Tuesday. He spoke on condition of anonymity because he was not authorized to talk to reporters.

Turkey's state-run Anadolu Agency said Wednesday that a convoy of trucks carrying howitzers and other ordinance reached the border town of Kilis, on the Turkish side, to "reinforce" units stationed at the border.

Northern Syria is awash with rival forces and state powers competing for influence over territory captured from the retreating Islamic State group.

The U.S.-backed Kurdish forces have clashed repeatedly with the Turkish-backed opposition forces, prompting at various instances Russia, the United States and Damascus to come between the sides to maintain peace.

But in a major escalation, the U.S. shot down a Syrian fighter jet it said was targeting its Kurdish allies on Sunday. That same day, Iran's powerful Revolutionary Guards fired six ballistic missile strikes against Islamic State-held territory in eastern Syria, hitting the city of Deir el-Zour.

The airstrike was in retaliation for an IS attack earlier in June on Iran's parliament and a shrine in Tehran that killed 18 people and wounded more than 50.

There have been few details of what the strikes achieved. The Guard claimed on Wednesday that the missiles had killed more than 170 IS militants, including several commanders. The claim could not be independently verified.


Associated Press writer Amir Vahdat in Tehran, Iran, contributed to this report.