Iranian President Hassan Rouhani said on Saturday that "terrorists" were applauding his United States counterpart Donald Trump for launching a missile strike on an airbase of his Syrian government ally.
"Once the ISIS threat has been reduced or eliminated, I think we can turn our attention directly to stabilizing the situation in Syria", he said.
Tillerson meets with Russian Foreign Minister Sergei Lavrov on Tuesday, just days after the United States fired cruise missiles at a Syrian air base in retaliation for the chemical attack.
Syria's ally Russian Federation says the deaths were caused when a Syrian air strike hit a depot where rebels were making chemical weapons, leading to a leak of toxic gas.
The missile strike also showed the Trump administration's willingness to break from Vladimir Putin. USA officials said Russian Federation bears responsibility for backing Assad and extending the six-year-old conflict, raising tension between the former Cold War rivals to the highest level since President Donald Trump took office in January.
Haley said the airstrikes destroyed an airfield from which the United States believes the chemical attacks on the rebel-held town of Khan Sheikhun were launched.
"It's very hard to understand how a political solution could result from the continuation of the Assad regime", McMaster said.
The defence secretary said Moscow must be part of the solution to ending the "needless suffering" of Syrian civilians.
"Someone who uses barrel bombs and chemicals to kill his own people simply can not be the future leader of Syria".
McMaster continued, insinuating that he believed Russian Federation had to be knowledgeable of Syria's plan to launch a chemical attack.
Italy, Germany, France, Britain, Canada and Japan are likely to use the G7 summit in Tuscany to tackle Mr Tillerson about U.S. policy on the Middle East. Almost 80 people died in Khan Sheikhoun town in the rebel-held northern province of Idlib on 4 April after Syrian planes allegedly carried out gas attacks, which the USA said was the banned nerve agent sarin.
"But neither regime change nor a full-on, unauthorized war against Syria is what we should be doing", Kaine said.
Haley reiterated the comments of Rex Tillerson, the USA secretary of state, who insisted that defeating Islamic State was the priority for the White House.