The Islamic State (IS) fighters ended the week in control of about half of Syrian territory. IS now controls "more than 95,000 square kilometres (38,000 square miles) in Syria, which is 50 percent of the country's territory," the Syrian Observatory for Human Rights based in Britain said.

The jihadists have taken Ramadi, capital of Anbar province, and the ancient Syrian city of Palmyra in the past week. Their gains come despite eight months of US-led air strikes.

The United Nations said on Friday at least 55,000 people have fled Ramadi alone since mid-May. The Security Council voiced "grave concern" for the UNESCO World Heritage site of Palmyra and for civilians trapped in the city.

There were reports that IS militants had hunted down Syrian government troops and loyalists in Palmyra, executing up to 280 in public as a warning, and imposing their strict interpretation of Islam on both men and women. A curfew from 5pm until sunrise local time was also imposed.

According to a priest in Damascus, a Christian priest, Jacques Mourad was kidnapped from the village of Qaryatayn, southwest of Palmyra and taken to an unknown location.

The IS militants were also reported to be making efforts to gain the support of opponents to President Bashar al Assad. They said they would repair electricity and water grids.

Barrel bombs

There were reports that Syrian aircraft had dropped barrel bombs near the military security headquarters at the northern edge of Palmyra's ancient ruins. The Iraqi government said it planned a counter-offensive in the western Anbar province involving Iranian-backed Shiite militia. The Pentagon said on Friday that coalition aircraft launched five strikes against IS in Syria and 15 against the jihadists in Iraq in the previous 24 hours.

The Syrian Observatory said the next target for IS appeared to be the Tayfour air base near Palmyra, where many government troops had retreated.

IS fighters had 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 allow free passage for weaponry and reinforcements across the border.

The UN World Food Program is taking food assistance into Anbar province to help tens of thousands of people who have fled the latest fighting.

UNESCO chief Irina Bokova called the first and second century Palmyra ruins "the birthplace of human civilisation", adding: "It belongs to the whole of humanity and I think everyone today should be worried about what is happening."

Also on Friday, IS claimed responsibility for an attack on a mosque in Saudi Arabia.

jm/rc (AP, AFP)