Pope Francis has decried the death of dozens of people in Syria from chemical poisoning as the top Catholic bishop in the US said the carnage 'shocks the soul'.

The Pope offered his prayers 'for the victims and their families,' adding: 'I appeal to the conscience of those who have political responsibility, locally and internationally, so that this tragedy may come to an end and relief be brought to that beloved population who for too long have been devastated by war.'

Cardinal Daniel DiNardo, the president of the US Conference of Catholic Bishops, said yesterday: 'The chemical attack in Syria on April 4 shocks the soul. The many innocent lives targeted by these terrible tools of war cry out for humanity's protection.'

At least 70 people, including children, were reportedly killed in Idlib, Syria on Tuesday by deadly gas after the neighborhood of Khan Sheikhoun was bombed. The attack reportedly came from forces of the Syrian President Bashar al-Assad.

There have been around 200 reported chemical attacks in Syria, according to the medical care group UOSSM.

Last year, the UN reported that Syrian government forces and ISIS had illegally used chemical weapons on multiple occasions in 2014 and 2015.

'If confirmed, this would constitute the single largest chemical weapons attack in [Syria] since the attack on Eastern Ghouta in August 2013,' Kim Won-Soo, the UN's High Representative for Disarmament Affairs, said of this week's incident.

UOSSM, which had doctors working in the targeted area, said that victims of Tuesday's bombing were showing symptoms of asphyxiation, foaming of the mouth, and 'severe Dyspnoea'.

The group stated: 'Medical facilities are overwhelmed with patients and unequipped to handle chemical attacks of this magnitude...many area hospitals have been put out of service, further complicating the situation.'

The president of UOSSM USA, Dr. Monzer Yazji reported seeing a 'major shortage in doctors, staff, and facilities inside Syria' during a visit there last week. 'The attack today has left us all paralyzed. We are unable to properly treat the injured,' he said.

The Reuters news agency reported that one activist witness said white smoke covered the vicinity after a bomb dropped.

The Syrian government has denied using chemical weapons on the area, and its Russian allies have claimed that a bomb hit a rebel-held factory manufacturing chemical weapons, which then dispelled the gas.