U.S. Senator John McCain, an advocate for a tougher stance on Syria for years, on Tuesday demanded the end of Damascus' "murderous rampage" saying Moscow should cease its support for the regime.

A U.S. strike on a Syrian air base is no substitute for a proper investigation and accountability after a devastating suspected chemical weapons attack, Amnesty International's chief said on Tuesday.

France still wants the U.N. Security Council to adopt a draft resolution demanding an investigation of the suspected chemical attack in Syria after it failed to agree on such a measure, the ambassador said Tuesday.

Turkey said on Tuesday that tests proved the deadly nerve agent sarin was used in a suspected chemical attack in northwestern Syria which killed dozens last week.

Russia's foreign minister will host three-way talks with his counterparts from Syria and Iran this week, Moscow said Tuesday, after the U.S. launched strikes against Syrian forces.

G7 foreign ministers have failed to agree on whether fresh sanctions should be imposed on Syrian President Bashar al-Assad or his ally Russia, Italy's Foreign Minister Angelino Alfano said Tuesday.

Russia said Tuesday it was hoping to avoid confrontation and engage in "constructive cooperation" with Washington as Secretary of State Rex Tillerson headed to Moscow. 

G7 foreign ministers insist there can be no peace solution for war-torn Syria with President Bashar al-Assad in power, French Foreign Minister Jean-Marc Ayrault said Tuesday.

Russian President Vladimir Putin on Tuesday warned of future chemical weapons "provocations" in Syria to frame President Bashar al-Assad, just as Washington's top diplomat arrived for talks in Moscow. 

"We have information from various sources that such provocations -- I cannot call them otherwise -- are being prepared in other regions of Syria, including in the southern outskirts of Damascus, where they are again planning to throw some kind of substance and accuse Syrian official authorities of using it," Putin said at a televised press conference.

Russia's defence ministry said Tuesday that two soldiers acting as military instructors to government troops in Syria had been killed by rebel forces.