Ukrainian authorities have opened a criminal case into treason following a now-abandoned proposal for a joint online conference with Russian state television to help end the war in eastern Ukraine.

Ukraine’s NewsOne channel and Russia’s state-run Rossia 24 broadcaster planned to host a videolink dialogue between ordinary citizens of the countries before the Ukrainian broadcaster canceled it over threats. The idea, which belonged to Viktor Medvedchuk, a prominent member of Ukraine’s Russia-leaning opposition, was welcomed by the Kremlin but caused major backlash in Kiev.