European Union leaders have backed U.K.'s assessment that the nerve agent attack on a former Russian double agent was almost certainly carried out by Moscow, saying, "there is no plausible alternative explanation."

Speaking in Brussels, Dutch Prime Minister Mark Rutte said it was "highly likely Russia is responsible," for the attack on 66-year-old Sergei Skripal and his daughter, Yulia, 33, at a shopping mall in southern England on March 4.

Britain's Prime Minister Theresa May won the backing of 27 other EU leaders at a summit Thursday. The bloc called the attack a "grave challenge to our shared security" and announced that it was recalling its ambassador to Russia.

May said of the EU support: "This is about us standing together to uphold our values against the Russian threat."

Although Rutte said there were no specific sanctions discussed at the summit, the EU said in a statement that it would "coordinate on the consequences to be drawn in the light of the answers provided by the Russian authorities."

The poison involved in the attack has been identified as Novichok, a military-grade nerve agent that was developed in a top-secret laboratory in Moscow in the 1980s and would be extremely difficult or impossible to obtain elsewhere.

Russia has repeatedly denied any involvement in the attack, calling the charges against it "crazy allegations."

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