Gunmen in Syria released three Red Cross staffers and a Red Crescent volunteer who had been kidnapped in ­rebel-held territory, the international agency said Monday.

The fate of three other Red Cross workers also seized Sunday in the northwestern Idlib province remained unclear, the International Committee of the Red Cross said.

Syrian opposition activists said the seven aid workers were taken at a rebel checkpoint outside the town of Saraqeb, manned by an al-Qaeda affiliate, the Islamic State of Iraq and Syria. There was no claim of responsibility.

About two dozen miles away, near Turkey, a car bomb went off Monday in the market of the town of Darkoush while it was crowded with people shopping for the four-day Muslim holiday of Eid al-Adha. The blast set cars on fire and sent people running.

The Britain-based Syrian Observatory for Human Rights said 27 people were killed. Another activist group, the Local Coordination Committees, put the death toll at 15.

It was not clear who carried out the bombing or why civilians were targeted in a rebel-held area. The use of car bombings in the conflict has increased, but most have been carried out against regime targets, usually by jihadi fighters among the rebels.

Meanwhile, Syria became a full member Monday of the Organization for the Prohibition of Chemical Weapons in another step toward eliminating its chemical weapons stockpile by mid-2014.

The mission is overseen by the OPCW and the United Nations. The joint team has inspected five of at least 20 sites in the past two weeks, according to the OPCW chief.

Ahmet Uzumcu signaled that the team of 60 OPCW inspectors and U.N. staffers is encountering difficulties. He was quoted as saying that one abandoned site was in rebel-held territory and that in other cases, routes went through opposition-controlled areas, preventing access because rebels have not promised cooperation.

The areas “change hands from one day to another, which is why we appeal to all sides in Syria to support this mission, to be cooperative and not render this mission more difficult,” Uzumcu  told the BBC. “It’s already challenging.”

The OPCW won the Nobel Peace Prize last week in a strong endorsement of its Syria mission.

U.N. Secretary-General Ban Ki-moon, meanwhile, selected Sigrid Kaag, a Middle East expert from the Netherlands, to head the joint OPCW-U.N. team in Syria, U.N. diplomats said. Kaag is an assistant administrator of the U.N. Development Program and speaks Arabic, said the diplomats, who spoke on the condition of anonymity ahead of a public announcement.

The push to eliminate Syria’s stockpile of about 1,000 metric tons of blister and nerve agents stems from an Aug. 21 chemical-weapons attack on opposition-held suburbs of Damascus. Hundreds were killed, including many children. The West says the Syrian government is responsible, while Damascus blames the rebels.

Syrian President Bashar al-
Assad said Monday that his country stopped manufacturing chemical agents in 1997 because they became an “outdated deterrent.” He said Syria has since concentrated on its missile capabilities.

Damascus is believed to have thousands of long-range missiles that can reach targets almost anywhere inside Israel, its archenemy.

“Developing Syria’s missile deterrent force that can be used from the first moments of war ended the necessity of chemical weapons,” Assad was quoted as saying in the Lebanese newspaper al-Akhbar.

Nonetheless, Assad said, Syria is suffering a “moral and political loss” in handing over its chemical weapons.

— Associated Press