Pakistan’s Nobel laureate and rights activist Malala Yousafzai has called on world leaders to end the devastating war in Syria that has claimed the lives of thousands.

“Chemical strikes like the toxic gas attack in Idlib on Tuesday​ ​have become a sickeningly routine as the Syrian conflict persists,” she said in a statement issued in wake of a horrific attack in the war-torn country.

“This morning innocent men, women and children suffered painful, senseless deaths,” read the statement.

Malala asked the international community to “do everything in your power to help the victims and end the war”.

The war, she said, had displaced millions. “This war has forced too many families from their homes, too many children from their schools and taken too many innocent lives. This war must end.”

Tuesday’s chemical attack killed at least 58 people, including 11 children, in the northwestern province of Idlib, a monitor, medics and rescue workers in the rebel-held area said.

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

The Syrian Observatory for Human Rights said the attack, believed to have been carried out by Syrian army jets, caused many people to choke, and some had foam coming out of their mouths. All the children were under the age of eight.

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

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

The air strikes that hit the town of Khan Sheikhoun, in the south of rebel-held Idlib, killed at least 58 people, said the Observatory, a British-based war monitoring group.

Warplanes later struck near a medical point where victims of the attack were receiving treatment, the Observatory and civil defense workers said.

The civil defence, 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 the capital in August 2013. Western states said the Syrian government was responsible for the 2013 attack. Damascus blamed rebels.