(Reuters)

At least 48 people were killed Saturday in the Syrian border town of Azaz when a truck bomb ripped through a busy ­marketplace.

Footage from the rebel-held area showed residents running from the blast site, some holding small children, as black smoke and the din of car alarms filled the air.

The Syrian Observatory for Human Rights, a Britain-based group collating reports from Syria, said the explosion came from a fuel or water tanker truck. Six of the dead were rebel fighters, it said. The rest were civilians.

There was no immediate claim of responsibility for the attack, which came amid a stuttering ­nationwide cease-fire backed by Turkey and Russia, now two of the most important diplomatic powers in Syria’s five-year-old war.

Located along the Turkish border some 20 miles north of Aleppo, Azaz was held by Islamic State militants for six months in 2013, and the group has been blamed for several attacks in the area since it was pushed out by a rebel offensive.

A image taken from a video obtained by Reuters at the scene of the explosion on Jan. 7. (Reuters TV/Reuters)

Further east along the border, Turkey is backing a rebel advance on the Islamic State stronghold of al-Bab. U.S. officials said they believe Ankara is trying to create a 5,000-square-mile area occupied by neither the extremist group nor Kurdish forces, which the Turkish government considers terrorists.

Saturday’s blast came hours after Turkey said it had completed a fresh round of airstrikes against Islamic State targets, killing 21 fighters and destroying buildings and vehicles.

Khalil Abdulrahman, 42, said the driver of the suicide vehicle had plowed through a rebel checkpoint and headed directly for the market and a nearby courthouse.

“Only civilians work in that place. There were so many killed, so many injured,” he said.

According to Jumaa Rahhal, a local health official, at least 140 people were wounded in the attack.

Azaz’s population has swelled over the past year as thousands of people fled pro-government offensives around Aleppo. Three Iraqi refugees were among those killed Saturday, Rahhal said. 

The city’s opposition-affiliated media center said Saturday that search-and-rescue operations continued for hours after the blast, which shattered the facade of a local courthouse.

Rescue workers attend to those injured in the blast on Jan .7. (Saif Alnajdi/Associated Press)

As the death toll rose, local hospitals put out an emergency call for blood donors and Turkish media outlets reported that 53 people had been carried across the border for treatment.

Abdulrahman said he combed the rubble of nearby shops for bodies.

“One was a school student,” he said. “I could only identify him by the notebook in his rucksack.”

Zakaria Zakaria in Istanbul contributed to this report.