Beirut (Reuters): A suspected gas attack, believed to be by Syrian government jets, killed at least 58 people including 11 children under the age of eight in the northwestern province of Idlib on Tuesday, a war monitor and medical workers in the rebel-held area said.

A Syrian military source strongly denied the army had used any such weapons.

The attack caused many people to choke or faint, and some had foam coming out of their mouths, the Syrian Observatory for Human Rights said, citing medical sources who described it as a sign of a gas attack.

The air strikes on the town of Khan Sheikhoun, in the south of rebel-held Idlib, also wounded more than 60 people, said the Observatory, a British-based war monitoring group.

"This morning, at 6:30 a.m., warplanes targeted Khan Sheikhoun with gases, believed to be sarin and chlorine," said Mounzer Khalil, head of Idlib's health authority, adding that the attack had killed more than 50 people and wounded 300.

"Most of the hospitals in Idlib province are now overflowing with wounded people," he told a news conference in Idlib.

Warplanes later struck near a medical point where victims of the attack were being treated, the Observatory said and civil defense workers said. The civil defense, also known as the White Helmets - a rescue service that operates in opposition areas of Syria - said jets struck one of its centers in the area and the nearby medical point.

It would mark the deadliest chemical attack in Syria since sarin gas killed hundreds of civilians in Ghouta near Damascus in August 2013. Western states said the Syrian government was responsible for that attack. Damascus blamed it on rebels.

The Syrian military source on Tuesday denied allegations that government forces had used chemical weapons, dismissing the accounts as rebel propaganda. The army "has not and does not use them, not in the past and not in the future, because it does not have them in the first place", the source said.

A joint inquiry for the United Nations and the global chemical weapons watchdog has previously accused government forces of toxic gas attacks. France called for an emergency UN Security Council meeting about Tuesday's suspected attack.