ISIL has released a video purportedly showing two captured Turkish soldiers being burned alive, after Ankara vowed to fight "terror" in Syria in response to 16 of its troops being killed in battle.

The 19-minute video, showing two uniformed men being hauled from a cage before being bound and torched, was posted online and was supposedly shot in the ISIL-declared "Aleppo Province" in northern Syria.

Speaking in Turkish, the killer of the two men criticises Turkish President Recep Tayyip Erdogan and calls for "destruction to be sowed" in Turkey.

The shocking images recall the killing of Moaz al-Kassasbeh, a Jordanian fighter pilot who was captured by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group when his plane went down in Syria in December 2014, and was later burned alive in a cage.

The ISIL-linked news agency Amaq said last month that the group had kidnapped two Turkish soldiers, and the Turkish army separately said it had lost contact with two of its men.

'Social media blocked'

Access to Twitter, YouTube and Facebook was reportedly blocked in Turkey after ISIL released the footage.

Turkey Blocks, a website that seeks to "identify and validate reports of internet mass-censorship events" reported users having problems accessing the three websites following the release of the video.

"The blocks each appear to be implemented at the ISP level, with each provider applying its own controls, hence some users may be partly or fully unaffected," it said.

"The shutdown is the second in a week, with another similar blackout following the assassination of Russia’s ambassador to Turkey."

The video's release comes a day after 16 Turkish soldiers were killed by ISIL fighters in Ankara's biggest loss so far in its unprecedented incursion into Syria.

They were killed in a succession of attacks around the Syrian town of Al-Bab on Wednesday which included three suicide car bombings.

The heavy toll showed the intensifying battle for the town, which Turkish forces have been seeking to capture for weeks in the biggest test of their four-month incursion into Syria.

Turkish troops entered Syria on August 24 in support of pro-Ankara Syrian rebels, with the aim of ousting ISIL as well as Kurdish militia from the border area.

At least 38 Turkish soldiers have been killed in the operation, which the Turkish government has dubbed Euphrates Shield.

Speaking earlier on Thursday, Erdogan vowed no let-up in the ongoing campaign.

"Yes, maybe we will have to lay martyrs to rest," he said in a speech in Ankara.

"But we are determined to preserve their memory and protect what they left us and continue this struggle." 

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Source: Al Jazeera and news agencies