The comments from the Trump administration signal a new course in the foreign policy regarding Syria.
"The president thanked the Prime Minister for her support in the wake of last week's U.S. military action against the Assad regime".
"The Prime Minister and the president agreed that a window of opportunity now exists in which to persuade Russian Federation that its alliance with Assad is no longer in its strategic interest". "So, really, now what happens depends on how everyone responds to what happened in Syria, and make sure that we start moving towards a political solution, and we start finding peace in that area".
"They also discussed the broader Middle East, including the threat posed by Iran throughout the region".
The US president's spokesman Sean Spicer warned on Monday that further action would be considered in certain circumstances.
The move came as Foreign Secretary Boris Johnson warned that senior Russian military officers involved in co-ordinating President Assad's campaign of repression against his own people could face worldwide sanctions.
During his first day in Italy, Tillerson plans to meet Monday with foreign ministers from the United Kingdom and France before the G-7 summit formally opens. Why they are supporting a regime that is committing mass murder against its own people.
"We have to learn the lessons of the past and learn the lessons of what went wrong in Libya when you choose that pathway of regime change".
"They have a choice".
The US and United Kingdom are expected to tell Russian Federation it must stop supporting the regime of Syrian President Bashar al Assad and instead help with drawing up a plan to rebuild the country.
If Syria carries out more chemical attacks, he said, "that is going to be clearly very damaging to US-Russian relations". "As I said again, taking this action I support and was important".
Assad accused the United States of trying to boost the morale of "terror groups" in Syria. "Other countries have to ask themselves some hard questions".
An arm of Lebanese militant group Hezbollah, meanwhile, issued a statement it said was on behalf of Russia, Iran and its allies, vowing to "reply with force" to any future aggression "in a variety of ways". "In fact, we were prepared to do more two days ago", McMaster said.
The president is not intimidated by Moscow's talk of war, his son said. "If we would want to appeal rationally to Russia", McMaster said.
"He is not a guy who gets intimidated".
Dozens of representatives of the media, local authorities, and emergency services have visited the airfield since the attack, with no alleged "storage units" or chemical weapon shells being found, the ministry said in a statement, calling on a mission of professional experts to be sent to the air base.
Trump acts decisively in Syria: Now what?
"If there was anything that Syria did, it was to validate the fact that there is no Russian Federation tie".
Several lawmakers said Sunday that decision shouldn't entirely be up to Trump.