The EU has recalled its ambassador to Moscow in the strongest signal yet that the bloc will rally behind the U.K. to punish Russia for the attempted murder of former spy Sergei Skripal. Leaders of all 28 EU countries—including the U.K., which remains inside the bloc for the time being—issued a statement saying there was “no plausible alternative explanation” for the nerve-agent attack on British soil other than Russia being responsible. Amid strained relations with the U.K. as the country negotiates its exit from the bloc, the European Council added in its statement: “We stand in unqualified solidarity with the United Kingdom in the face of this grave challenge to our shared security.” The EU said its Moscow ambassador would be recalled “for consultations.” In response, Vladimir Putin’s spokesman, Dmitry Peskov, said Friday that Russia “doesn’t understand” the EU’s decision, and said the Kremlin would study what measures the bloc had taken before deciding what response to take.