But he also clarified there had been "no change to our military posture" in Syria following a retaliatory USA strike against a Syrian airbase, and that Washington's "first priority" in Syria was to defeat the Islamic State terror group.
The strike completed a policy reversal for President Donald Trump - who once warned America to stay out of the conflict - and drew angry responses from Damascus and its main ally, Russia.
Trump said that the attack was a response to the alleged chemical weapon use in Syria's Idlib province on Tuesday, which resulted in the death of over 80 people.
Mr Trump said he had ordered the firing of 59 tomahawk cruise missiles to "degrade" and "dissuade" the Syrian regime in the letter to the House of Representatives and the Senate.
McMaster characterized Thursday's USA airstrike on a Syrian airfield as an opportunity for Russian Federation to reevaluate its continued support for Syrian President Bashar Assad, adding that addressing both Assad's actions and routing ISIS could be done simultaneously.
"I hope Russian Federation is thinking carefully about its continued alliance with Bashar al-Assad, because every time one of these horrific attacks occurs, it draws Russian Federation closer into some level of responsibility", Secretary of State Rex Tillerson said Sunday on ABC. "Those days are over", the USA ambassador to the UN, Nikki Haley, told a special session of the UN security council.
"I think what the United States and our allies want to do is to enable the Syrian people to make that determination", Tillerson told CBS.
Tillerson said he sees no reason for retaliation from Russian Federation for the US missile strikes. "The United States will not stand by when chemical weapons are used".
Given all of this, Sanders reiterated that Trump needs congressional approval to take further military action on Syria, or any other country, for that matter, The Hill reported.
McCain: Trump administration 'partially to blame' for Syria chemical attack
President Donald Trump , before his election, described fighting ISIS and seeking Assad's removal at the same time as "idiocy". From Italy, Tillerson will travel to Moscow, becoming the first Trump administration official to visit Russian Federation .
"This is part of the problem with Syria, Russia's sponsorship of [Syrian President Bashar al-Assad's] murderous regime".
Mr Tillerson said on Sunday that Russia's inaction had allowed the chemical attack to take place.
Asked if Mr. Trump was considering slapping tougher sanctions on Russia, Ms. Haley said such moves are now under consideration.
He will say that Assad has no future in Syria, Russia must stop supporting the regime and a plan to rebuild the country must be drawn up.
The Kremlin said in a statement Rouhani also spoke with Russian President Vladimir Putin by phone.
The United States is now likely to be more aggressive in pursuing intelligence about Syria's suspected chemical weapons programme.
Before last week, Mr. Trump opposed action against Mr. Assad's Russia-backed regime and framed the Syria problem as an issue of eliminating the Islamic State. Meanwhile, Tillerson suggested that the airstrikes hadn't really changed priorities toward ousting Assad.
'Today we call on all parties to get back to the table and get a deal done, ' the British defence minister said.
Russian Federation said Mr Johnson's decision showed a lack of understanding of events in Syria and claimed there was little point in speaking to Britain anyway as it was "in the shadow" of its partners.
Comments