ISTANBUL — Four more Turkish soldiers have been killed in northern Syria, the Turkish military said late Saturday, bringing the day’s death toll to 11 in what has been the most lethal day since Ankara’s offensive on Syrian Kurdish militias began.

Turkey’s President Recep Tayyip Erdogan announced earlier that a military helicopter was “downed” in the Afrin operation. Erdogan didn’t mention by name the Syrian Kurdish People’s Protection Units, or YPG, but hinted they were to blame.

The country’s prime minister walked back on the comments soon after, saying the cause of the helicopter’s crash was not yet clear.

“We don’t have exact evidence or documents to determine that it went down with any outside interference,” Binali Yildirim told reporters in the western province of Mugla.

The Turkish military said that two soldiers were killed when its attack helicopter crashed and was destroyed around 1 p.m. local time. A technical team launched an investigation.

A spokesman for the Kurdish militia said his fighters downed the chopper in Raju, northwest Afrin.

In a video posted online by the YPG-dominated Syrian Democratic Forces, a helicopter is seen flying over a tree-lined hill and another helicopter is captured during its crash. A helicopter is seen firing two rockets as plumes of smoke from the crash rise over the trees.