The international chemical weapons watchdog is to send a fact-finding mission to the Syrian town where a suspected gas attack took place, killing more than 40 people over the weekend.

In a statement, the Organisation for the Prohibition of Chemical Weapons (OPCW) said a fact-finding team was "preparing to deploy to Syria shortly".

It comes after the OPCW received a request from the Syrian government and its Russian backers to investigate the allegations.

Syrian opposition activists, rescue workers and medics say more than 40 people were killed on Saturday in a suspected chemical attack on Douma, the last rebel-held town in the Eastern Ghouta region.

The bodies of families were reportedly found suffocated in their homes and shelters.

Chris Deerin: Syria’s children, and our own, will suffer because of the West's inaction

Reports suggested more than 500 people, mostly women and children, were brought to medical centres with difficulty breathing, foaming at the mouth, and burning sensations in the eyes.

The Syrian government and its Russian backers strongly deny the allegations, and have questioned whether a chemical weapons attack took place.

The OPCW said its technical secretariat has asked the Syrian government to make the necessary arrangements for the deployment of a fact-finding mission.

The group is the implementing body for the Chemical Weapons Convention of 1997, which has been signed by 192 member states.

Syria became a member in 2013 as part of a deal brokered by the US and Russia after a chemical attack in eastern Ghouta killed hundreds of people. That attack was widely blamed on government forces, who denied responsibility.

UN secretary-general Antonio Guterres said he was outraged by the reported attack, and that the use of chemical weapons would be a violation of international law. He also reaffirmed his support for an OPCW investigation.

Chris Deerin: Syria’s children, and our own, will suffer because of the West's inaction

The OPCW will need Russian government cooperation to visit the site of the attack, which is now under Syrian government control.

There is now growing anticipation that retaliatory US strikes may be launched imminently in response to the suspected attack from the weekend.

The White House confirmed Donald Trump had cancelled his first trip to Latin America to "oversee the American response" to the situation.

Moscow's ambassador to the UN, Vassily Nebenzia, warned of the potential consequences to Western intervention in Syria, saying that US attacks "could lead to grave repercussions".

Syrian government forces were on high alert and taking precautionary measures at military positions across the country.

The Britain-based Syrian Observatory for Human Rights said that as of Monday night, troops had been on a 72-hour alert and are fortifying their positions.

Chris Deerin: Syria’s children, and our own, will suffer because of the West's inaction

On Monday, Russia and the Syrian military blamed Israel for a pre-dawn missile attack on a major Syrian air base, killing 14 people.

Though Israel does not typically comment on its operations in Syria, and it is unclear whether the missile attack was linked to the alleged use of chemical weapons.