U.S. Secretary of State Mike Pompeo on Tuesday said he was "deeply concerned" by initial findings that Russian opposition leader Alexei Navalny was poisoned, and endorsed a European Union-led investigation into the circumstances of his illness.
It was the first formal statement issued by Pompeo since Navalny collapsed on a plane last week while returning to Moscow from Siberia.
Navalny, a leading critic of Russian President Vladimir Putin, on Sunday was airlifted in a coma for treatment at a clinic in Berlin, where doctors found indications of a toxic substance in his body.
"The United States is deeply concerned by reported preliminary conclusions from German medical experts that ... Navalny was poisoned," Pompeo said. "If the reports prove accurate, the United States supports the EU’s call for a comprehensive investigation and stands ready to assist in that effort."
"Navalny’s family and the Russian people deserve to see a full and transparent investigation carried out, and for those involved to be held accountable," Pompeo said.
His statement came after the Kremlin said it saw no reason for now for an investigation and that the German clinic's findings were not yet conclusive.
German Chancellor Angela Merkel on Monday called for an investigation and said Russia should hold the perpetrators accountable. The top EU diplomat on Tuesday called for such a probe, a stance echoed on Tuesday by the U.S. ambassador to Moscow, John Sullivan.