Activist groups in Syria reported Wednesday that the government had launched another suspected chemical attack in the country’s northwestern province of Idlib, leaving about a dozen people suffocated.

Several Syrian activist groups have said that government helicopters dropped at least two barrel bombs containing chlorine on the town of Saraqeb, leading to cases of suffocation, the Associated Press (AP) reported, adding that the local reports could not be independently verified.

According to the Syrian Network for Human Rights, at least 12 victims were “suffocating” due to the poisonous barrel bombs dropped on the city on Wednesday.

Khaled Khoja, the head of the Syrian National Coalition, the country’s main opposition group in exile, said he had asked the U.N. Security Council to take necessary actions. Last month, the council adopted several resolutions, including one which threatens action against chemical attacks in Syria, the AP reported.

Meanwhile, the council members have asked the Organization for the Prohibition of Chemical Weapons (OPCW) to look into the latest attacks.

The OPCW, which recently condemned the use of chlorine in Syria as a breach of international law, said in a report last month that it had destroyed two Syrian chemical weapons facilities, and that the remaining 12 facilities would be dismantled by the summer.

The U.S. and other members of the U.N. Security Council have repeatedly blamed the Syrian government for launching chemical attacks, arguing that no one else in the country’s four-year civil war has helicopters to deliver the deadly chemicals, the AP reported.