G7 foreign ministers will attempt to agree a common position on the Syrian conflict, before the US secretary of state flies to Russia to try to persuade it to abandon its Syrian ally.
Rex Tillerson will also meet officials from allied Middle Eastern countries before heading to Moscow.
The UK has suggested threatening tightly focused sanctions on Russian and Syrian military officers.
The moves follow the latest apparent use of chemical weapons in Syria.
Syria has denied it carried out a chemical attack on the rebel-held town of Khan Sheikhoun last week that left 89 people dead.
Reports overnight quoted a senior US official as saying that the Russians knew of the chemical attack because a drone had been flying over a hospital in Khan Sheikhoun as victims sought help.
Hours later a jet bombed the hospital in what the US believed was an attempt to cover up the attack, the Associated Press agency said.
Meanwhile, US Defence Secretary James Mattis has given fresh details on the retaliatory strike against Syria’s Shayrat airbase last Thursday.
He said the “measured response” by the US – which saw 59 Cruise missiles fired – had “resulted in the damage or destruction of fuel and ammunition sites, air defence capabilities and 20% of Syria’s operational aircraft”.
The Syrian military admits significant material damage but a Russian defence ministry spokesman said only six Syrian Air Force MiG-23s, plus a number of buildings, were destroyed and that only 23 of the missiles had reached Shayrat.
Mr Tillerson broadened his consultations in Italy on Tuesday morning, with key regional allies including Saudi Arabia, Jordan, Qatar and Turkey joining the G7 governments meeting in Italy.
The US hope is that a UK proposal of new tightly focused sanctions could win approval – sanctions against named senior officers in both the Russian and Syrian armed forces accused of targeting civilians.
BBC diplomatic correspondent James Robbins says British officials recognise that the imposition of more general sanctions on Russia has previously been resisted by Italy and Germany, but they hope this narrower approach could get backing and provide Mr Tillerson with political ammunition to take to Moscow.
Downing Street says that when President Trump and the British Prime Minister Theresa May talked on the phone on Monday night, they agreed a window of opportunity existed to persuade Russia its alliance with Assad was no longer in its strategic interest.
The problem for them remains that President Putin has never accepted that before, and still shows no sign at all of changing his position, our correspondent says.
Russia is already subject to a raft of sanctions imposed by the US and EU in response to the annexation of Crimea and the crisis in eastern Ukraine. President Obama expelled 35 Russian diplomats from the US in December 2016, in response to alleged hacking of the US election.
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