So-called Islamic State (IS) has released a video online which claims to show two captured Turkish soldiers being burned alive.
IS said they were killed in revenge for Turkish killing of Muslims.
Turkey launched a campaign against IS in northern Syria in August and is currently fighting IS around the group's stronghold of al-Bab.
The video has not been independently verified. There has so far been no comment from Turkey.
The Turkish army previously reported losing contact with two soldiers in northern Syria last month but it is unclear whether either are the men in the video.
At least one of the purported victims appears to have been captured by the group as far back as September 2015.
Turkish officials did not immediately respond to the publication of the video late on Thursday.
IS released the video through a number of its online accounts and through the messaging app Telegram.
It showed the two men, dressed in camouflage, caged in open countryside. The pair, collared and chained, were taken from the cage and made declarations to camera before being killed.
Several reports suggested that Turkey had limited access to social media sites such as Twitter and YouTube following the release of the footage. However, many users reported no interruption.
Earlier this week, 16 Turkish soldiers were killed near al-Bab, in the biggest loss for Turkish forces fighting the IS group in the region.