European Union foreign ministers agreed to sanction Russia over Moscow’s involvement in the poisoning of opposition leader Alexei Navalny, according to diplomatic sources.

The 27 ministers had reached an agreement in a meeting in Luxembourg to start work preparing measures to correspond with the proposals made last week by France and Germany, which said Moscow was responsible for the poisoning of Navalny with the Soviet-developed nerve agent Novichok.

Both Germany and France believe that Navalny’s poisoning could only have happened with the involvement of Russian authorities. Berlin and Paris say they have not had a credible explanation from Moscow for what the Organisation for the Prohibition of Chemical Weapons said was the presence of Novichok in Navalny’s body.