G7 foreign ministers are looking to send a "clear and coordinated message" to Russia over its stance on Syria as the US ratcheted up the pressure following a suspected chemical attack in the war-torn country.



The UK's Foreign Secretary Boris Johnson set the tone for the meeting, describing Syrian President Bashar al-Assad as "toxic" and saying it was "time for [Russian President] Vladimir Putin to face the truth about the tyrant he is propping up".

Foreign ministers from the Group of Seven main industrialised countries are meeting in the Italian town of Lucca for two days before US Secretary of State Rex Tillerson flies to Moscow on Tuesday.

The agenda is 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 was the first time the US has intervened directly against Assad's government, which 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 Tuscan city of Lucca groups foreign ministers from the US, Britain, Canada, France, Germany, Italy and Japan.

'End Assad support'

Washington's retaliation was slammed by Iran and North Korea and put it on a direct diplomatic collision course with Moscow, where Tillerson will travel for talks with his Russian counterpart Sergey Lavrov.



The US stepped up the pressure on Sunday on Russia to rein in the Syrian government, warning that any further chemical attacks would be "very damaging" to their relationship and suggesting any peace deal would be difficult with Assad in power.



Tillerson enraged Moscow by asking if it was possible Russia did not know about Syria's chemical arms, and called on the country to fulfil the obligation it made to the international community to guarantee the elimination of the weapons.

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"We need to make it clear to Putin that the time to back Assad has gone," Johnson said on Monday, warning that Putin was "damaging Russia" by supporting Assad.

He had cancelled a scheduled visit to Moscow "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 past week are never repeated".



Tillerson would "deliver that clear and coordinated message to the Russians", he said.

Italy has arranged a last-minute meeting on Tuesday between the G7 ministers and their counterparts from Jordan, Qatar, Saudi Arabia, Turkey and the United Arab Emirates.

Italian media said the aim was "to avert a dangerous military escalation".