He also called on Russia to reconsider its support for his regime
The United States' Secretary of State Rex Tillerson has said there is"no doubt" that Bashar al-Assad's regime was responsible for the recent chemical attack in Syria.
As the Pentagon remains in detailed discussions with the White House about military options on Syria, Tillerson said that Assad's future as Syrian president is now uncertain.
"Assad's role in the future is uncertain, clearly, and clearly with the acts that he has taken it would seem there would be no role for him to govern the Syrian people," he said at a press conference this evening.
When asked if the US is considering the organisation of a international coalition to remove Assad from power, Tillerson said that "steps are underway".
He also called on Russia, a key ally of Assad, to reconsider its support for his regime.
Moscow has warned against apportioning blame until an investigation has been carried out, but a spokesman for
President Vladimir Putin did say earlier that Russia's support for Damascus is "not unconditional".
The Syrian government maintains it did not use chemical weapons, instead blaming opposition fighters for stockpiling chemicals which were hit in an airstrike on a weapons depot.
Discussions are continuing at the UN headquarters on a Security Council resolution that would condemn the attack.
Meanwhile, two Republican senators have called on President Trump to take out Syria's air force as part of a quick and forceful response.
John McCain and Lindsey Graham said Assad "has crossed a line" and "must pay a punitive cost for this horrific attack".
"This is a test of the new administration, but also for our entire country," the pair said in a statement.
"Assad is trying to see what he can get away with."
Senator Graham later said he does not think Mr Trump needs the approval of Congress to use military force in Syria.
"Hit this guy," he said of Assad. "You've got my full permission."