Islamic State (IS) militants have hunted down Syrian government troops and loyalists in the historic town of Palmyra, shooting or beheading them in public as a warning and imposing their strict interpretation of Islam, activists said.
The bloody purge, which relied mostly on informants, was aimed at solidifying the extremists' grip on the strategic town that was overrun by IS fighters on Wednesday and winning the support of President Bashar Assad's opponents, who have suffered from a government crackdown in the area in the last four years of Syria's civil war.
The strategy included promises to restore electricity and water grids after Palmyra was cleared of regime loyalists, according to an activist in the historic town known by the nom de guerre Omar Hamza, because he fears for his security.
The capture of Palmyra has raised alarm that the militants might try to destroy one of the Middle East's most spectacular archaeological sites - a well-preserved, 2,000-year-old Roman-era city on the town's edge - as they have destroyed others in Syria and Iraq.
For the moment, however, their priority appeared to be in imposing their rule, with activists saying there were no signs the group moved in on the ancient ruins.
Meanwhile in neighbouring Iraq, IS militants made more territorial gains, seizing the small town of Husseiba, less than a week after capturing the provincial capital of Ramadi, said tribal leader Sheikh Rafie al-Fahdawi.
They captured the Iraqi side of a key border crossing with Syria on Thursday after Iraqi forces pulled out. The fall of the al-Walid crossing in Anbar province will help the militants shuttle weaponry and reinforcements more easily across the border of the two countries where they have declared a self-styled caliphate.
The IS militants imposed a curfew in Palmyra from 5pm to sunrise and banned people from leaving town until this morning to ensure none of the government figures they seek manage to escape. Jihadis went through the streets telling residents via loudspeakers not to give refuge to Assad loyalists.
IS commanders also fanned out to Palmyra's mosques to deliver sermons during Friday prayers. Mosques were packed after fighters urged people to attend and told women to cover their faces.
The sermons were mostly about the importance of performing the five-times-a-day prayers in the mosques and women having to cover their faces and dress in loose clothes, Hamza said via Skype.
At the mosque where he prayed, the person delivering the sermon was a non-Syrian Arab, as were most of the leaders in the group in town, he said, while the fighters were Syrians.
In his sermon, the speaker warned that women not wearing the proper Islamic attire would be flogged.
Fighters were carrying out a bloody, door-to-door search to find and kill fugitive soldiers and known Assad loyalists, several activists said.
Prompted by the IS warnings not to provide shelter, some residents came forward with information about troops who had tried to melt into the population when the militants stormed the town, said another activist, who goes by the name Bebars al-Talawy.
Amateur video posted on a pro-IS Facebook page showed residents and militants gathering around two bloodied men in military uniforms on a Palmyra street.
"Let all the residents see them," one of the men shown in the video told an IS fighter. Photos circulating on the feeds showed purported government troops shot dead or decapitated.
Hamza and al-Talawy said as many as 280 loyalists and government soldiers were summarily killed, some shot in the head or beheaded in a public square.
Militants abducted soldiers and pro-government gunmen from homes, shops and other places where they had sought to hide, said al-Talawy, who is based in the nearby city of Homs.
"The search is going from house to house, shop to shop, and people on the streets have to show identity cards," said Osama al-Khatib, an activist from Palmyra who is now in Turkey.
He said some 150 bodies lay in the streets, including 25 members of the pro-government militia known as the Popular Committees.
The door-to-door hunt was similar to a purge the militants carried out in Ramadi after it fell on Sunday.
The United Nations Security Council condemned the "barbaric terrorist acts" and expressed deep concern for the thousands of people still in Palmyra after the takeover, especially women and children.
The council statement called for safe passage for people leaving the city and pointed out that "the primary responsibility to protect its populations lies with the Syrian authorities".
Gunmen believed to be from IS kidnapped a Christian priest, the Rev Jacques Mourad, from the village of Qaryatayn, south west of Palmyra. Mr Mourad, 48, and his bodyguard were taken to an unknown location, according to a priest in in Damascus.
UN special envoy for Syria Staffan de Mistura said he received with "deep sadness" the news of Mr Mourad's abduction.
Hamza said the public killings in Palmyra appeared aimed at winning support of residents who opposed Assad's rule, and that the strategy was succeeding with some.
"People don't seem to be resentful of the new guidelines. They are saying it is much better than the regime, which used to terrorise the whole town, especially through the arrest campaigns," he said.
He said electrical power - which had been out for 10 days as Syrian troops and IS militants battled - was partially restored.