BEIRUT — Suspected chlorine gas attacks by Syrian government helicopters injured some 40 people and killed a child in the country’s northwest, activists said Saturday, a day after an international chemical weapons watchdog said it was ready to investigate a series of newly claimed attacks.

Videos shared by the Syrian Civil Defense activist group showed medics and residents rushing children to a local hospital as they coughed, some gasping for air in Saraqeb, a town in Idlib province. A video from Nareb, another town in the province where a coalition of insurgent groups has made gains in recent days against troops loyal to President Bashar Assad, showed a medic receiving oxygen himself after rescuing people from another attack.

The videos appeared genuine and corresponded to other Associated Press reporting about the attacks.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of activists on the ground, said the attacks overnight Friday injured at least 40 civilians, including children. The Observatory said medical officials in Nareb said a child was killed, though the cause of death was not clear. The Local Coordination Committees, another activist group, also reported the suspected chemical attack in Saraqeb.

There was no mention of the attacks in Syrian state media.

Chlorine was first introduced as a chemical weapon in World War I with disastrous effects as gas masks were not widely available. While chlorine has many industrial and public uses, as a weapon it can choke victims to death.

Most nations banned its use in war in the Geneva Protocol of 1925. The U.S. and other countries have blamed Assad’s government of repeatedly of dropping chlorine from helicopters during the civil war, as no other force is flying them in the conflict. Forces loyal to Assad have blamed rebels for such attacks.

The suspected attacks come a day after The Associated Press obtained a report by the Organization for the Prohibition of Chemical Weapons saying a fact-finding team from the group is ready to look into multiple allegations of chlorine attacks in recent months. The Syrian government would need to approve the group’s visit.

Activists had reported a similar attack on Saraqeb on Wednesday.

The suspected chemical attacks come as government forces in Idlib province battle a joint insurgent campaign that has punctured the notion that Assad is on his way to defeating the four-year-old rebellion.

Meanwhile, Syrian rebels shelled government-held districts in the contested northern city of Aleppo on Saturday, killing 22 civilians and wounding 45 in an apparent retaliation for the killing of a leading rebel fighter a day earlier, Syrian state television reported.

The Observatory said rebel shelling on government-controlled areas killed at least 10 people, including three children. It said the numbers are likely to rise.

The discrepancy in casualty figures couldn’t be immediately reconciled but such differences are common in the immediate aftermath of attacks.

Aleppo, once Syria’s commercial hub, became a key front in the country’s civil war after rebels launched an offensive there in July 2012. The city has since been carved up into areas controlled by the government and others controlled by an array of rebel groups.

The shelling came after the killing Friday of prominent rebel leader Khaled Serag, known as Khaled Hayani, said Abu Riyad, an activist in Aleppo known by his nickname for fear of reprisal.

Riyad said Hayani was shot dead by a sniper. The Observatory confirmed Hayani was killed and said he was one of the first to fight against the Islamic State group when it moved into the area.

Also Saturday, the Observatory said at least 13 civilians, including six children, were killed when government aircraft struck the eastern province of Deir el-Zour, where the government is in fierce battles with Islamic State militants. The Local Coordination Committees reported seven civilian casualties in one location in Deir el-Zour.