Donald Trump has said he will soon make a decision, “probably by the end of today”, on how the US will respond to the latest alleged chemical attack by the Syrian government, adding that ”nothing is off the table” in terms of military action.

He condemned the reported poison gas attack in Douma, a rebel-held town in Syria, and said he was talking to military leaders and would decide who was responsible.

“I’d like to begin by condemning the heinous attack on innocent Syrians with banned chemical weapons,” the president said at the start of a cabinet meeting. “This is about humanity and it can’t be allowed to happen. If it’s the Russians, if it’s Syria, if it’s Iran, if it’s all of them together, we’ll figure it out.”

He added: “We are studying that situation extremely closely. We are meeting with our military and everybody else, and we’ll be making some major decisions over the next 24 to 48 hours.”

Dozens of civilians are believed to have died in the suspected poison gas attack over the weekend. UK Prime Minister Theresa May said that Syria’s president, Bashar al-Assad, and his Russian backers, must be “held to account” for the “barbaric” action if they are found to be responsible.

When asked if Russian President Vladimir Putin bears any responsibility for the reported attack, Mr Trump responded: “He may, yeah, he may. And if he does it’s going to be very tough, very tough.”

“Everybody’s gonna pay a price. He will, everybody will,” Mr Trump added.

The Syrian government has repeatedly blamed rebel groups for spreading false news in relation to such attacks, and Russian Foreign Minister Sergei Lavrov said allegations of a chemical attack were false and a provocation. Mr Lavrov said a strike on a Syrian base in the wake of the suspected attack was a dangerous development. Syria and Russia have blamed Israel for the attack on the air base.

Earlier in the day, Defence Secretary James Mattis said the US had not ruled out launching airstrikes against the Syrian government.

“I don’t rule out anything right now,” Mr Mattis said while hosting Sheikh Tamim Bin Hamad Al-Thani, the emir of Qatar, at the Pentagon.

Eastern Ghouta bombings: Syrian war in pictures Show all 14 1 /14 Eastern Ghouta bombings: Syrian war in pictures Eastern Ghouta bombings: Syrian war in pictures A Syrian woman and children run for cover amid the rubble of buildings. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Smoke rises from buildings following the attack on the village of Mesraba in the rebel-held besieged Eastern Ghouta region on the outskirts of the capital Damascu. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Injured children receive medical treatment. EPA Eastern Ghouta bombings: Syrian war in pictures A Syrian man carries a child injured. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures An injured child receives treatment following bombings on several areas of eastern Ghouta. EPA Eastern Ghouta bombings: Syrian war in pictures A child reacts inside a hospital after relatives were injured in the bombing. EPA Eastern Ghouta bombings: Syrian war in pictures Syrian children cry at a make-shift hospital in Douma following air strikes on the Syrian village of Mesraba. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Syrian Civil Defense group extinguishing a store during airstrikes and shelling by Syrian government forces. AP Eastern Ghouta bombings: Syrian war in pictures A wounded 12-year-old Syrian boy, cries as he receives treatment at a make-shift hospital. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Syrians carry a wounded man. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures An injured man covered with blood at a medical point. Reuters Eastern Ghouta bombings: Syrian war in pictures People sit a medical point in the besieged town of Douma, Eastern Ghouta. Reuters Eastern Ghouta bombings: Syrian war in pictures Syrian Civil Defense running to help survivors. AP Eastern Ghouta bombings: Syrian war in pictures Injured children receive medical treatment. EPA

Western allies have looked to increase pressure on the Kremlin for its relationship with Mr Assad, as calls increase for co-ordinated international action over the alleged chemical attack.

“The first thing we have to look at is why are chemical weapons still being used at all when Russia was the framework guarantor of removing all chemical weapons, and so working with our allies and partners from Nato to Qatar and elsewhere we are going to address this issue,” Mr Mattis continued.

The international chemical weapons watchdog opened an investigation on Monday into the attack. Chemicals have been used in other attacks suspected to have been carried out by the Syrian government.

The Organisation for the Prohibition of Chemical Weapons (OPCW) chief, Ahmet Uzumcu, said it was responding with “grave concern” to the suspected chemical weapons attack on Saturday in the town of Douma, in the Ghouta region.

The State Department said in a statement that it was consulting with allies on a response.

“There will be consequences for this unacceptable atrocity,” it said.

The Syrian government and its ally Russia have denied involvement in the attack.

But the US has renewed a push for the United Nations Security Council to establish a new inquiry into who is to blame for using chemical weapons in Syria.

The US circulated a revised draft resolution to the 15-member council, which it first put forward on March 1, amid a warning from Mr Trump that there would be a “big price to pay” for the suspected attack on Saturday.

A spokesperson for the UK Foreign Office said Foreign Secretary Boris Johnson spoke to Acting US Secretary of State John Sullivan about the attack. Their discussion followed Mr Johnson’s conversation with French Foreign Minister Jean-Yves Le Drian this morning.

“The Foreign Secretary and Acting Secretary of State agreed that, based on current media reports and reports from those on the ground, this attack bore hallmarks of previous chemical weapons attacks by the Assad regime,” the spokesperson said. “They reiterated their commitment to standing up for the Chemical Weapons Convention and to ensuring that those responsible for this horrific attack are held to account. They underlined the importance of the UK, the US, and France remaining in close touch.”