Isis in Palmyra: Civilians forced to watch execution of 20 men at amphitheatre

The Britain-based Syrian Observatory for Human Rights said the men were accused of having fought for President Bashar Assad's army. It is not known how they were killed.

The Unesco World Heritage site was overrun by militants last week, threatening the future of 2,000 year-old monuments and ruins. Thousands of Palmyra’s residents fled but many are still living within the city walls, while the UN human rights office in Geneva said it had received reports of Syrian government forces preventing people from leaving until they retreated from the city.

The group released an 87-second video through its media arms showing all of the ruins still intact on Wednesday.

Isis also released pictures of the notorious Tadmour prison on Thursday, which fell to militants along with Palmyra. The grim facility was where hundreds of political prisoners were held and allegedly tortured by the regime.

If these walls could talk.ISIS releases photos from Tadmor prison.No details on prison files or prisoners fate #Syria pic.twitter.com/48rab4viCl

; Nadim Houry (@nadimhoury) May 28, 2015

a rare photo of terrible #Tadmor jail after #ISIS took #Palmyre No confirmed info about #prisoners fate... pic.twitter.com/7tgv1ajjjI

; frederic Helbert (@FredericHelbert) May 27, 2015

The SOHR said a total of 67 civilians, including 14 children and 12 women, had been killed in the city of al- Sikhni, the village of al- Aamiriyyi, and in Palmyra for “dealing with the regime forces and hiding regime’s members in their houses”.

More than 230 men, women and children have been killed by militants in total since 16 May in Deir Ezzor and Palmyra. Isis is now in control of an estimated 95,000 square kilometres of land in Syria - more than half of the country.