By ZEINA KARAM ,  Associated Press

BEIRUT (AP) — Islamic State militants staged a surprise attack early Tuesday at a crossing frequently used by Iraqi and Syrian civilians seeking safety in northeastern Syria, killing at least 37 people, mostly civilians, Kurdish officials and activists said.
The militants struck before dawn after sneaking into the village of Rajm Sleibi, located along a front line that separates the Kurdish-controlled Hassakeh province from IS-held areas further south. Some militants reportedly blew themselves up at a Kurdish checkpoint while others attacked sleeping civilians in a nearby temporary camp sheltering hundreds of displaced people who fled IS-controlled territory.
The International Rescue Committee said thousands of people from the Iraqi city of Mosul have traveled west to the Sleibi crossing since October, often via smugglers. In a statement, it said several children were among the dead and wounded.
"It was three in the morning when Daesh came and started to shoot at people," said Abdulah Khalef Hamid, an Iraqi refugee from Mosul, who said his mother-in-law was killed in Tuesday's attack. "I was wounded and they thought I was dead so they left me. We were around 200 families, they left at sunrise," he added.
Daesh is the Arabic acronym for IS.
Redur Khalil, a spokesman for the main Kurdish fighting force in Syria, said the attack started with an early morning assault by IS militants on a checkpoint in Sleibi belonging to the Syrian Democratic Forces, a U.S.-backed and Kurdish-dominated force that fights IS.
The militants then "committed a massacre" against civilians as they sought to enter SDF-controlled territory, Khalil said.
He told The Associated Press the attack came a few hours after IS suicide bombers dressed in civilian clothes sneaked into the town of Shaddadeh and attacked SDF forces, triggering clashes that were ongoing.
Survivors from the attack on the camp said the militants arrived in four cars before shooting several people and kidnapping others.
"They were shouting 'You are infidels and you are going toward the infidels,'" said Fatima, a displaced Syrian woman who asked that her last name not be used, fearing retribution. "They shot at the checkpoint and at the civilians there, and they dragged the youngsters and put them in the cars and drove them away," she said.
Issam Amin, a media activist in Hassakeh, said the victims arriving at the city's hospitals had stabbing and gunshot wounds.
The Britain-based Syrian Observatory for Human Rights, which tracks the Syrian conflict through activists on the ground, said Tuesday's attack included suicide bombers and heavy clashes with the SDF. The Observatory put the death toll at 38, including 23 civilians, many of them Iraqi. Hawar, a news agency for the semi-autonomous Kurdish areas in Syria, put the death toll at 37.
The Islamic State group is under attack by an array of forces in Syria and Iraq.
In Syria, the SDF is now fighting to recapture the town of Tabqa, an important militant stronghold located about 40 kilometers (25 miles) southeast of the IS group's de facto capital, Raqqa. Kurdish officials said Kurdish-led opposition fighters have pushed the extremists almost completely out of Tabqa and were cleaning up the town. They said IS continues to hold the nearby dam on the Euphrates River.
In Iraq, the extremist group is fighting for survival against Iraqi forces and their allies in the last neighborhoods it still holds in the western part of Mosul, Iraq's second largest city.
IS claimed responsibility for Tuesday's attacks through its Aamaq media arm, saying its fighters attacked four Kurdish positions in the southern countryside of Hassakeh province.
Rajm Sleibi lies about 30 kilometers (18 miles) south of the town of al-Hol, which houses a large refugee camp for civilians displaced from Syria and Iraq. A Kurdish activist said it is the entry point to Hassakeh for Syrians civilians fleeing the eastern cities of Deir el-Zour and Raqqa, and those fleeing from Mosul and elsewhere in Iraq. The civilians spend about two weeks in Rajm Sleibi while they get security clearance from Kurdish authorities, and are then taken to al-Hol.
The activist spoke on condition of anonymity, fearing for his safety.
The camp is within the zone of influence of the SDF but not directly protected by its forces.
Elsewhere in Syria, opposition activists said IS killed 10 of its own after accusing them of selling weapons to arms traders. The activists said the killings took place in the Mayadeen area in eastern Syria, near the Iraqi border.
The Observatory and Omar Abu Laila, a Europe-based activist with contacts in the area, said the men were all Iraqis and were shot dead Monday in a main street in front of dozens of onlookers.