US President Donald Trump and his German and British counterparts have agreed that Moscow must be urged to halt links with Syria. Both Berlin and London have stressed their support for holding Assad's regime to account.
In phone calls with German Chancellor Angela Merkel and British Prime Minister Theresa May on Monday evening, Trump discussed last Friday's airstrikes on a Syrian air base in retaliation for what Washington says was a chemical gas attack by Syria's military.
The three leaders agreed "on the importance of holding Syrian President Bashar al-Assad accountable" for the atrocity, the White House said in a statement after the calls.
The Syrian government has denied it was behind the April 4 assault which killed as many as 100 people.
A spokeswoman for May said Washington and London had agreed that there was a "window of opportunity" to persuade Syria's longtime ally Russia to sever its links with Assad.
New talks hopeful
"They agreed that US Secretary of State Tillerson's visit to Moscow this week provides an opportunity to make progress towards a solution which will deliver a lasting political settlement," the spokeswoman said.
Tillerson is due in Russia on Wednesday, but will not meet Russian President Vladimir Putin, according to the Kremlin, a possible clue to the increasingly frayed ties between the two powers.
Meanwhile, British Foreign Secretary Boris Johnson on Monday floated the possibility of additional sanctions on Moscow and Damascus, despite Trump previously declaring a preference of removing embargos on some of Washington's foes.
Speaking on the sidelines of the G7 foreign ministers' meeting in Italy, Johnson warned Putin and Assad that Washington could intervene in the Syria conflict again.
"He [Putin] must understand that Assad is now toxic in every sense. He is poisoning the innocent people of Syria with weapons that were banned 100 years ago - and he is poisoning the reputation of Russia."
Last Friday's airstrikes destroyed "20 percent of Syria's operational aircraft," US Defense Secretary Jim Mattis said in a statement on Monday. The Syrian government has lost the ability to refuel or rearm aircraft at Shayrat, he added.
Moscow has condemned last week's US strikes, calling them "a flagrant violation of international law and an act of aggression."
Shift in strategy
The intervention marked a major shift in Washington's strategy towards the six-year conflict in Syria. Trump had previously been reluctant to intervene against Assad.
Some analysts believe he might now be ready to adopt a tougher-than-expected stance with the Syrian leader and his main backer, Russia.
That likelihood was backed up by White House spokesman Sean Spicer on Monday, who warned Syria against further use of chemical weapons or chlorine-laden barrel bombs.
"If you gas a baby or drop a barrel bomb onto innocent people, you will see a response from this president," Spicer said.
mm/jm (AFP, AP, dpa, Reuters)