Leaders of the seven leading global economies have asked Russia to stop supporting the regime of President Bashar Assad following an alleged chemical attack on Syrians.

Boris Johnson, the British foreign minister, said at a G-7 meeting in Italy on Monday evening that this was the moment for Russia to pick a side.

“I think it’s very important that in these circumstances for the world to present a united front and for that there to be absolutely no ambiguity about the message and the message we are sending to the Russians is very, very clear: Do they want to stick with a toxic regime, do they want to be eternally associated with a guy who gases his own people or do they want to work with the Americans and the rest of the G-7 and indeed many other countries for a new future for Syria,” Johnson told reporters at the end of the first day of the G-7 meeting.

The U.K and the U.S. are reportedly pushing for more sanctions on Russia but there’s speculation that other G-7 leaders are opposed to the idea. Italian officials, hosting the meeting, invited members from Saudi Arabia, the United Arab Emirates, Jordan and Turkey to participate in the discussions given their geopolitical importance when dealing with the Syrian war.

Turkey’s Foreign Minister Mevlut Cavusoglu said Tuesday his government has evidence that the Assad regime still has capacity to use chemical weapons. He urged his counterparts to agree on measures to prevent their use, Reuters reported.

The White House authorized the launch of 59 Tomahawk cruise missiles on Thursday evening in response to what President Donald Trump‘s administration and several U.S. allies claim was a chemical attack by the Bashar Assad regime which had left scores of people dead. This marked a shift in the U.S. administration’s strategy towards Russia and global politics.

On Monday night, British Prime Minister Theresa May had a phone conversation with Trump where they “agreed that a window of opportunity now exists in which to persuade Russia that its alliance with Assad is no longer in its strategic interest.”

International officials have hardened their tone when addressing Russia, including members of Trump’s administration, which had seemed more “Russia-friendly” than previous governments. U.S. Secretary of State Rex Tillerson, who met Russia’s President Vladimir Putin when he led Exxon Mobil, described Assad’s regime as “murderous” on Monday and vowed to dedicate his work to “holding to account any and all who commit crimes against the innocents anywhere in the world.” Last Thursday, Tillerson said Russia had “failed in its responsibility” to remove Syria’s chemical weapons as agreed in 2013 and therefore it was either supporting the chemical attack or it had been “incompetent” in doing what it had agreed to.

Meanwhile, Russia has denied the claims of a chemical attack and said the U.S. intervention last week was illegal and that it would not be exchanging information with Trump’s administration.

Tillerson is due to meet his Russian counterpart on Wednesday. According to Reuters, he will seek a commitment in which Russia agrees to eliminate the chemical weapons in the Syrian regime.

The Syrian war has been ongoing since 2011.

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