Islamic State militants have abducted at least 220 people from Assyrian Christian villages in northeastern Syria during a three-day offensive, a monitoring group that tracks violence in Syria said on Thursday.
The British-based Syrian Observatory for Human Rights said the abductions took place when Islamic State captured 10 villages inhabited by the ancient Christian minority near Hasaka, a city mainly held by the Kurds, in the past three days.
Islamic State has ruthlessly targeted members of religious minorities, as well as fellow Sunni Muslims who refuse to swear allegiance to the 'caliphate' it has declared in parts of Syria and Iraq.
A video released last week showed its members beheading 21 Egyptian Coptic Christians in Libya. Last August it killed or enslaved hundreds of Iraq's Yazidis, whom it considers devil worshippers.
The militants have previously used kidnappings to trade captives for their own captured fighters but it was not clear if they planned to use the same tactic with the Assyrians, whose abduction they have not yet claimed.
The United States on Wednesday condemned the attacks on Assyrian Christian villages, which it said included the burning of homes and churches and abduction of women, children and the elderly.
Hundreds of Christians have now fled to the two main cities in Hasaka province, according to the Syriac National Council, a Syrian Christian group.
The region is strategically important to Islamic State as one of the bridges between land it controls in Syria and Iraq. In recent weeks it has lost ground in northeast Syria after being pushed out of the Kurdish town of Kobani in January by Kurdish forces backed by U.S.-led airstrikes.
These same strikes, however, have been unable to stop its advance into smaller villages.
Heavy fighting continued through Wednesday night between Syrian Kurdish militants and Islamic State, Kurdish officials and the human rights observatory said.
"ISIS now controls 10 Christian villages," observatory head Rami Abdulrahman said by phone, using an acronym for Islamic State. "They have taken the people they kidnapped away from the villages and into their territory," he said.
Two Kurdish officials said around 90 people had been abducted. One of the officials, Nasir Haj Mahmoud, from the YPG militia in northeastern Syria, said they were taken to Shedadeh village, which is Islamic State territory. "Some Assyrian villages are still under Islamic State control," he said.
Mahmoud said YPG had cut a main road linking Tel Hamis with al-Houl, a town just a few miles (kilometres) from the Iraqi border, and prevented attempts by Islamic State to reopen it. "The YPG are still in control," he said.
He said dozens had died overnight in clashes, which underline the emergence of well-organised Syrian Kurdish militia as the main partner for the U.S.-led alliance against Islamic State in Syria.
Islamic State fighters also launched an attack on rival insurgents east of Damascus, the group said on social media on Thursday, a rare skirmish near the southern capital from the militant organisation, which is strongest in the northeast.
An official Twitter account for Islamic State said its fighters ambushed members of the Free Syrian Army, an alliance of western-backed rebels, on Wednesday in the Eastern Ghouta area.
It said the FSA suffered casualties, and Islamic State fighters seized tanks and ammunition in what it called a strategic location close to the government stronghold of central Damascus. The Observatory confirmed the attack but said it had targeted rival jihadist brigades.
Mainstream rebels fighting President Bashar al-Assad's forces in Syria's civil war have mostly been eclipsed by jihadists, complicating a U.S. plan to train and equip Syrian opposition forces to fight Islamic State.
Units from Islamic State are staging increasing attacks in the south, mostly in the Qalamoun Mountain range that runs north-south to Damascus and also borders Lebanon.
The Lebanese army deployed along that border on Thursday near the village of Ras Baalbek and fired artillery at jihadists who move between Syria and Lebanon, a Lebanese security source said.