The suspected gas attack on the rebel-held town of Douma prompted international outrage at the weekend, with an emergency meeting of the UN Security Council scheduled to take place on Monday afternoon.
Doctors in the town, outside Damascus, reported battling to save people who arrived from 7.45pm on Saturday presenting symptoms of a possible toxic gas attack.
The news prompted US president Donald Trump to lash out at Russia and Iran on social media, describing the Syrian leader, Bashar al-Assad, as an “animal”.
The US president also warned on Sunday that the regime and its supporters would pay a “high price” for the alleged use of chemical weapons.
British foreign secretary Boris Johnson urged the international community to respond to the “truly horrific” incident, but Britain’s main opposition party has been criticised for its weak response to the attack.
In a statement which failed to apportion blame, Labour said that “anyone found responsible for using chemical weapons is brought to justice”.
The statement said Syrian people had “suffered for too long from the atrocities and brutality of this war, whether committed by the Assad regime, by Jihadist militias, or by their respective international supporters”.
Labour’s statement in full:
“The horrifying images and reports that have emerged from Douma point to an attack using chemical weapons, in blatant contravention of international humanitarian law, with young children among the many victims.
“As the Foreign Office has said, it is vital and urgent that there is a full and independent investigation of this reported attack, and that anyone found responsible for using chemical weapons is brought to justice. It is also equally vital and urgent to re-establish the recent ceasefire across Eastern Ghouta, agree a safe exit for the militias occupying Douma and any civilians who want to leave, and provide humanitarian relief and medical aid for all those civilians remaining in the city.
“And ultimately, there must be concrete steps on all sides to re-start meaningful talks on a political solution and lasting peace in Syria. The Syrian people have suffered too long from the atrocities and brutality of this war, whether committed by the Assad regime, by Jihadist militias, or by their respective international supporters, and it is time for that suffering to stop.”
Tory cabinet minister Sajid Javid slammed what he said was a press release that “could have been written by the Kremlin”.
“No mention at all of Russian and Iranian complicity,” Javid added. “How did a once great party come to this?”
Labour leader Jeremy Corbyn later tweeted: “The horrific deaths and injuries in Douma point to a chemical attack which must be fully investigated by the UN and those responsible held to account.
“The need to restart real negotiations for peace and a political settlement in Syria could not be more urgent.”
Some Labour frontbenchers issued their own statements.
Shadow Brexit secretary, Sir Keir Starmer, said on Twitter: “Bombing is not the answer. But we cannot just look away: concerted and effective international response needed.”
Shadow education secretary Angela Rayner said: “Indiscriminate bombing of civilian areas, the targeting of hospitals and medical centres, starving civilians as a weapon of war along with the alleged horrific use of chemical weapons are war crimes and there must be a day of reckoning for those responsible.”
The Assad government strongly denies that poison gas was used on the rebel-held town of Douma.
According to reports, families were found suffocated in their homes and shelters, with foam on their mouths.
Reports suggested more than 500 people, mostly women and children, were brought to medical centres with breathing difficulties.