"We are considering an appropriate response for this chemical weapons attack which violates all previous UN resolutions, violates international norms and long-held agreements between parties, including the Syrian regime, the Russian Government, and all other members of the UN Security Council," Tillerson told reporters at the West Palm Beach airport in Florida.
"It's a serious matter; it requires a serious response," he said in response to a question at the West Palm Beach Airport on his way to Mar A-Lago to attend the US-China Summit meeting.
"Assad's role in the future is uncertain, clearly. And with the acts that he has taken, it would seem that there would be no role for him to govern the Syrian people," he said indicating that Assad's days are numbered.
Tillerson said the events that have occurred in Syria along with the Tuesday's chemical weapons attack have just "horrified all". It has also brought to the front pages and to television screens, the tragedy, that is part of the Syrian conflict, he said.
More From This Section
And I think further, it is very important that the Russian Government consider carefully their continued support for the Assad regime," Tillerson said.
The White House said the US President Donald Trump is being presented with a lot of options on how to deal with the Syrian situation.
"He is being presented with a lot of options. I would go back and echo the comments the president made in the Rose Garden. He is not one to telegraph those decisions until he is ready to make them,"White House Press Secretary Sean Spicer told reporters travelling with Trump aboard Air Force One.
He is scheduled to meet his national security team in Mar a-Lago where he is to attend meetings with the visiting Chinese counterpart Xi Jinping.