Turkish President Recep Tayyip Erdogan has pledged to launch a military offensive in northern Syria in the coming days after Washington announced it would pull its military contingent out of the region.

Ankara needs to show restraint and avoid military action in Northern Syria, Islamic Republic News Agency quoted Iran's President Hassan Rouhani as saying.

"Turkey is rightfully worried about its southern borders. "We believe that a correct path should be adopted to remove those concerns... American troops must leave the region... Kurds in Syria... should support the Syrian army," Rouhani said.

Meanwhile, the Iranian Students News Agency reported that Iran's military had launched an unannounced military exercise near the country's border with Turkey.

According to the report, rapid reaction units, mobile and offence brigades, and helicopters from the Army Ground Force's Air Unit are involved in the drill.

The reports emerged as Ankara is gearing up for an offensive in Iran-allied Syria to clear the northern region of the country of Kurdish militants along its border.

The Turkish Defence Ministry announced on Tuesday that Ankara had completed preparations for its military incursion. 

The United States, meanwhile, has started to withdraw its troops from the area. The White House stated it would not "support or be involved in" Turkey's upcoming operation.