G7 foreign ministers were on Monday to send a "clear and coordinated message" to Russia on Syria as Washington upped the pressure following a suspected chemical attack in the wartorn country.
Top diplomats from the seven major advanced economies are in Italy for their annual two-day meeting which had initially been expected to focus on intimate talks with new US Secretary of State Rex Tillerson about hotspots like Libya, Iran and Ukraine.
But the agenda is now likely to be dominated by last week's suspected chemical weapons attack on a rebel-held Syrian town that killed at least 87 civilians, and the US cruise missiles fired at a Syrian air base in retaliation.
It marked the first time Washington has intervened directly against the regime of President Bashar al-Assad, who is fighting a civil war with the backing of Russia and Iran, and the G7 ministers will deliberate the West's next steps.
The gathering in the Italian city of Lucca, which begins at 1430 GMT, groups foreign ministers from the US and Britain, Canada, France, Germany, Italy and Japan.
The US diplomacy chief arrived in Tuscany late Sunday and briefly met Japan's Foreign Minister Fumio Kishida Monday morning before attending a WWII memorial at the site of a Nazi massacre in Sant'Anna di Stazzema near Lucca.
Tillerson was then to hold a series of bilateral talks before the start of the G7 meeting.
Washington's retaliation was slammed by Iran and North Korea and put it on a direct diplomatic collision course with Moscow, where Tillerson heads on Tuesday for talks with his Russian counterpart Sergei Lavrov.
Italy has arranged a last-minute meeting on Tuesday between the G7 ministers and their counterparts from Turkey, the United Arab Emirates, Saudi Arabia, Jordan and Qatar.
Italian media said the aim was "to avert a dangerous military escalation".
Britain's Johnson cancelled a scheduled visit to Moscow Monday, saying his priority was now "to continue contact with the US and others" ahead of Tillerson's Russian trip.
He called on Russia to do "everything possible to bring about a political settlement in Syria and work with the rest of the international community to ensure that the shocking events of the last week are never repeated".
Tillerson would "deliver that clear and coordinated message to the Russians", he said.