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"The prime minister noted that the use of a nerve agent against Yulia and Sergei Skripal in Salisbury was a grave attack on the sovereign territory of the UK, and the first use of nerve agents on European soil since the Second World War," a spokeswoman said in a statement.
On Syria, the spokeswoman said May had told Xi that "Russia's blocking of diplomatic action underlined the importance of the international community working together to re-establish an independent mechanism that attributes responsibility to the perpetrators of attacks such as the one in Douma."