Donald Trump has vowed to respond ”forcefully” to a suspected chemical weapons attack in Syria, as Russia warned US military action would be met with “grave repercussions.”

President Trump told a meeting of military leaders and national security advisers he would make a decision on a response by Monday night “or very shortly after.”

He said the United States had “a lot of options militarily” on Syria.

“But we can’t let atrocities like we all witnessed... we can’t let that happen in our world... especially when we’re able to because of the power of the United States, the power of our country, we’re able to stop it.”

He added: ”We have a lot of options militarily, and we’ll be letting you know pretty soon. Probably after the fact.”

Syria civil war: Footage shows children treated following chemical weapons attack in Douma

The Syrian government was accused of being behind an alleged chemical weapons attack which killed at least 60 people late on Saturday, with more than 1,000 injured at several sites in Douma, a rebel-held town in eastern Ghouta, near Damascus, according to a Syrian aid organisation.

President Trump’s comments came after Moscow’s ambassador to the UN warned of potential consequences of Western intervention in Syria

Nikki Haley, the US ambassador to the UN, accuses Russia of having 'the blood of Syrian children' on its hands (DON EMMERT/AFP/Getty Images)

During heated exchanges at the UN Security Council, Vassily Nebenzia said US attacks on Syria “could lead to grave repercussions.”

The US ambassador, Nikki Haley, accused Russia of having “the blood of Syrian children” on its hands.

Mr Nebenzia dismissed claims the Syrian regime had used chemical weapons as “fake news” as he called for inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) to fly to Syria on Tuesday to visit the site of the alleged attack.

Ms Haley urged the UN to take action, but stressed whether it acts or not “either way, the United States will respond”.

She added: “Meetings are ongoing. Important decisions are being weighed, even as we speak.”

The Russian ambassador to the UN, Vassily Nebenzia, discusses threats to international peace and security at an emergency Security Council session (DON EMMERT/AFP/Getty Images)

When Mr Trump was asked if Russia’s president, Vladimir Putin, bore any responsibility for the attack, he responded: ”He may, yeah, he may. And if he does it’s going to be very tough, very tough.” He added: “Everybody’s gonna pay a price. He will. Everybody will.”

He criticised Mr Putin by name on Twitter, as he castigated Russia and Iran for backing Bashar al-Assad, who he called an “animal.”

Almost exactly a year ago, the US fired cruise missiles at a Syrian air base in response to the killing of dozens of civilians in a sarin gas attack on the opposition-held town of Khan Sheikhoun.

The missile strikes did little long-term damage to Syrian government forces, and Mr Assad’s position has only became stronger with Russian and Iranian support.

Amid the discussions in the White House, the US military appeared to manoeuvre into position to carry out any attack order.

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

The USS Donald Cook, a guided missile destroyer armed with Tomahawk cruise missiles, was underway in the eastern Mediterranean after completing a port call in Cyprus.

President Trump and his French counterpart, Emmanuel Macron, spoke twice in less than 24 hours to coordinate their response, the White House said.

Mr Macron and Mr Trump reiterated their desire for a “strong reaction” from the international community, Mr Macron’s office said.

Theresa May said that the UK was considering what action was necessary in response to the “barbaric” attack.

Asked if the UK would join any US-led military action in Syria, the prime minister said: “What we are currently doing is working urgently with our allies to assess what has happened here.

“We... are working urgently with our allies to asses what has happened. But, we are also working with our allies on any action that is necessary.”

A child receiving oxygen through respirators following an alleged poison gas attack in the rebel-held town of Douma (AP)

Ms May sidestepped a question on whether Parliament would be recalled from recess to debate any military intervention.

William Hague, the former Conservative foreign secretary, said he had “little doubt” if he was still in office he would recommend military action in Syria.

Lord Hague, who was foreign secretary when then prime minister David Cameron lost a Commons vote he wanted to back action in Syria, said the aftermath of the defeat left the UK “enfeebled spectators of one of the most destructive conflagrations of our time”.

In February, the current foreign secretary, Boris Johnson, said Britain should consider joining military action against the Syrian regime if there is fresh “incontrovertible” evidence it has used chemical weapons against its own people.

Mr Johnson discussed the situation with the acting US secretary of state, John Sullivan, twice on Monday.

Video shows missiles over Homs, Syria as airstrikes hit the country following chemical weapons attack

The US State Department said Mr Johnson and his Washington counterpart discussed “potential further steps the US and UK governments might take in coordination with other partners”.