Shocking images have emerged of the mass execution of Iraqi soldiers detained by militants from the jihadist group Islamic State of Iraq and the Levant.

The photographs, released on one of ISIL’s own Twitter feeds, show dozens of Shiite soldiers being driven in trucks to a rural area where they are forced to lie facedown in the dirt with their hands tied behind their back.

In the next frame, a Sunni militiaman appears to execute them in a hail of automatic gunfire that kicks up the dirt near their heads. The next frame shows a pile of lifeless bodies.

Earlier on Saturday ISIL announced on Twitter it had executed 1700 Shiite soldiers, but human rights groups have not yet been able to confirm their claim.

The release of these images – which have also not been verified but appear to be legitimate – indicates the Sunni militants have killed many soldiers, possibly near the town of Tikrit, 150 kilometres north of the capital Baghdad.

An ISIL-aligned account by the name of @w_salahadden boasts about 27,800 followers and has tweeted just over 1,000 times in recent months.

In one of the most recent posts, a flattened body lies face down on a footpath, coagulating streams of dark blood snaking down the gutter. Two men purported to be members of ISIL are standing over the body. One has a hand reaching towards the corpse, another his foot resting on it.

Twitter has been locked in a pitched battle with social media-savvy ISIL  members for almost a week. It has already shut down a number of accounts. Publishing violent images and messages on Twitter violates the site’s policies. Any user can flag content as offensive.

The Iraqi Ministry of Communications has reportedly shut down social media in Baghdad and other parts of the country, apparently in an attempt to prevent ISIL from using platforms such as Facebook, Twitter and YouTube to promote its violent activities.

This is not the first time the popular micro-blogging site has been used to cover violence.

In September 2013, terrorists attacking Kenya’s West Gate Mall in Nairobi sent frequent updates to the social media site, which was scrambling to shut down the accounts as more sprung up.

Militants seized Tikrit last week after first taking control of Iraq’s second largest city, Mosul, in a lightening-fast offensive that prompted Iraqi soldiers to lay down their weapons and immediately cede control of the city.

Human rights groups say up to 500,000 people have fled Mosul since ISIL took control, fearing both the strict Islamic state ISIL is attempting to establish as well as the retaliatory air strikes they believe the government of Nouri al-Maliki is preparing to launch.

The International Organisation for Migration estimated another 40,000 people had fled Tikrit and Samarra following militant attacks.

The offensive is part of ISIL’s plan to establish a Sunni Islamist state that runs from Iraq across the border into Syria and beyond.

On Thursday, United Nations High Commissioner for Human Rights Navi Pillay expressed alarm at reports of summary executions and extrajudicial killings, calling for an immediate cessation of violence.

“There will be particular scrutiny of the conduct of ISIL, given their well-documented record of committing grave international crimes in Syria,” she added, noting that the Commission of Inquiry on Syria has accused ISIL of committing crimes against humanity in Raqqa, Idlib and Aleppo.

With Rose Powell