Aleksei Navalny, the Russian opposition leader who is recovering from being poisoned, has spoken to a German prosecutor about the attempt on his life and says he plans to return to Russia as soon as he has recovered.

The news came hours after the German government announced that laboratories in France and Sweden had confirmed that the substance used to poison Mr. Navalny was a form of the nerve agent Novichok, results that match Berlin’s findings and provide additional confidence that the Russian state was involved.