At least 37 people, including dozens of civilians, have been killed in an attack by ISIL fighters targeting a crossing along Syria's northeastern border with Iraq, according to a monitoring group.

The Britain-based Syrian Observatory for Human Rights said five suicide bombers detonated explosives before dawn on Tuesday in Rajm al-Salibi, a village in Hasaka province that is home to a temporary camp sheltering hundreds of displaced people.

The explosions were followed by gun battles between other ISIL attackers and US-backed Kurdish fighters of the Syrian Democratic Forces (SDF) at a nearby checkpoint, leaving dozens of people wounded.

"The area where the attacks took place is where many refugees escaping violence in Iraq were gathering," Rami Abdel Rahman, the head of Observatory, told the DPA news agency, adding that the attackers might have come from Iraq.

The Observatory monitors Syria's conflict via a network of contacts on the ground.

'They thought I was dead'

The International Rescue Committee said thousands of people from the Iraqi city of Mosul, where Iraqi forces have been battling ISIL fighters, have travelled west to the Rajm al-Salibi crossing since October, often via people 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," Abdulah Khalef Hamid, an Iraqi refugee from Mosul, told the Associated Press news agency, using an Arabic acronym for ISIL.

"I was wounded and they thought I was dead so they left me. We were around 200 families, they left at sunrise," he said, adding that his mother-in-law was killed in the attack

Nasser Haj Mansour, an adviser to the SDF, confirmed to the Reuters news agency that several civilian casualties included people who fled ISIL from Syria's Deir Az Zor and Iraq.

Redur Khalil, a spokesman for the main Kurdish fighting force in Syria, told AP the attack came a few hours after ISIL suicide bombers dressed in civilian clothes sneaked into al-Shadadi town and attacked SDF forces, triggering clashes.

ISIL, which stands for Islamic State of Iraq and the Levant, and is also known as ISIS, said that a group of 16 fighters had launched an attack on Kurdish checkpoints, killing and wounding dozens.

It said some ISIL fighters carried out four attacks inside al-Shadadi which mainly targeted military posts, while others carried out attacks inside Hariri village and a sixth squad hit the barracks at Rajm al-Salibi.

The attacks came as Kurdish fighters backed by the US-led, anti-ISIL coalition continued their mission in the town of Tabqa, which sits on a strategic supply route about 55km west of Raqqa, the de facto capital of ISIL in Syria.

"After taking the old city, we now control around 90 percent of Tabqa ... we advanced against the ISIL and pushed further to the other parts of the city," Jihan Sheikh, of the Ghadab al-Furat, a Kurdish group fighting under the SDF, told Al Jazeera on Tuesday.

The SDF, an alliance of Kurdish and Arab militias, has seized large swaths of northern Syria from ISIL in a campaign to drive the group out of Raqqa.