US Vice President Mike Pence says “all options are on the table” in response to the chemical attack
The US President Donald Trump has suggested the US may take on a more forceful role in Syria after a devastating chemical weapons attack that killed at least 72 people.
He told a news conference that the attack was an “affront to humanity” that had changed his attitude to dealing with the conflict.
President Trump said the atrocity - which he blamed on Syrian President Bashar al Assad - "crossed many, many lines," but he stopped short of saying how he would tackle the crisis.
In an interview with The New York Times, the President also said Moscow's role in the long-running civil war was "disappointing" - adding it was a "very sad day for Russia because they're aligned".
It comes after his vice president Mike Pence said “all options are on the table” in response to the attack and US Secretary of State Rex Tillerson warned America was in "no doubt" that the embattled Syrian government was responsible for the attack.
The comments come a matter of days after several senior Trump administration officials said they were no longer focused on removing Mr Assad from power.
The Syrian government has denied responsibility for the attack while Russia is objecting to a UN draft resolution condemning it.
Moscow is threatening to veto the resolution the resolution, which it claims is based on “fake” information and is “anti-Syrian.”
Moscow has insisted that Syrian rebels were behind the attack in Idlib province.
Russian officials said they believed the poison gas contamination was the result of a leak from a rebel chemical weapons depot hit by government airstrikes - a theory described by a senior White House official as not credible.
Britain's ambassador to the United Nations, Matthew Rycroft, has also challenged Moscow to stop supporting the regime, and said: "What is your plan? What is your plan to stop these horrific senseless attacks? We had a plan and we had the support and you rejected it to protect Assad."
Meanwhile, the US ambassador to the UN appeared to threaten possible unilateral action if the Security Council "fails in its duty to act collectively."
Two US officials told the Associated Press that preliminary reports indicate the attack likely involved chlorine and traces of sarin.
If nerve agent was used, this would suggest Syria has reneged on a deal to give up chemical weapons.
Footage from the attack in the town of Khan Sheikhoun showed people convulsing and foaming from the mouth, with medics using hoses to wash chemicals from victims' bodies - many of them children.
President Trump now faces the same dilemma as his predecessor Barack Obama.
In his first statement following Tuesday's attack, he had claimed the "weakness" of the Obama administration had enabled the Assad regime.
Openly challenging Moscow would mean Mr Trump risks deep involvement in a Middle East war by seeking to punish the Syrian government for using banned weapons.
Compromising and accepting Mr Assad's continued grip on power however, could cause his administration to look weak.
Mr Trump's latest remarks have given some rebels cautious optimism that America's approach towards the civil war may be about to change - but others believe it is too early to tell whether any meaningful policy shift is forthcoming.
In the White House Rose Garden, Mr Trump had said: "When you kill innocent children, innocent babies - babies, little babies - with a chemical gas that is so lethal, people were shocked to hear what gas it was, that crosses many, many lines."
Fares al Bayoush, a Free Syrian Army commander, told the Reuters news agency: "(His) statement contains serious difference from the previous statements, and we expect positivity … from the American role."
Additional reporting from IRN ...