Islamic State fighters are tightening their grip on the historic city of Palmyra in Syria, days after capturing the provincial capital of Ramadi in neighbouring Iraq.
A monitoring group says the jihadists now control half of Syria after more than four years of conflict that grew out of an uprising against President Bashar al-Assad.
The United Nations has received reports that Syrian forces in Palmyra prevented civilians from leaving, ahead of its fall to IS militants, and of summary executions.
Islamic State has also overrun the World Heritage site adjacent to the modern city, raising concerns about its future. The militants have previously demolished ancient sites that pre-date Islam.
A spokeswoman for the UN in Geneva said the organisation believed about a third of the 200,000 residents of Tadmur, the Arabic name for the modern settlement next to Palmyra, had fled.
Many were only able to flee on Wednesday and Thursday, once Syrian government forces themselves had left and IS took over the city, said Ravina Shamdasani.
Syrian state media said pro-government forces had pulled out after "assuring the evacuation" of "most" of the inhabitants of Tadmur.
An activist who has family members in Palmyra told the BBC that his relatives wanted to flee but there was no way out.
IS fighters were searching the city for Syrian army soldiers, he said, and residents were being warned via mosque loudspeakers not to hide them. Ms Shamdasani said the UN also believed IS had been carrying out door-to-door searches in the city.
The activist said inhabitants were angry that Western media were focusing on the ancient ruins, and not the population.
UN cultural organisation Unesco says its destruction would be "an enormous loss to humanity", but no damage has been reported there yet.
Unesco director-general Irina Bokova appealed to all sides to preserve the "incredible vestiges of human history." Protecting sites like Palmyra had become a security imperative, as well as a cultural concern, because, she said, the militias were using trafficked artefacts to get funds.
Setbacks in Iraq, Libya
In a new setback for government forces in Iraq, IS fighters have overrun defences east of Ramadi.
The defensive line was breached at Husaiba, about 10 km from the city, on Thursday afternoon after IS fighters intensified mortar and rocket fire.
Ramadi fell to the insurgents on Sunday in the most significant setback for Iraqi security forces in nearly a year.
Fighters loyal to the Sunni Muslim group have also consolidated their grip on the Libyan city of Sirte, home town of the former leader Muammar Gaddafi.
The United States is acknowledging Islamic State victories in Iraq and Syria in the past week as a setback.
But President Barack Obama insists America is not losing the war with IS, and he continues to resist
Republican Party calls for the US to send in ground troops.
The Pentagon plans delivery of extra weaponry to Iraq as early as next week - 2000 anti-tank rockets are to be sent, 1000 more than previously announced.
A spokesperson said the rockets would help defend against suicide bombers driving vehicles packed with explosives, a tactic used by IS fighters to help them seize Ramadi.
- BBC / REUTERS