MOSCOW (AP) — The investigative organization Bellingcat claimed Wednesday that Russian agents who had tailed opposition leader Alexei Navalny before his poisoning also shadowed a journalist who had earlier fallen severely ill with similar symptoms.

Dmitry Bykov, an author and journalist who is an outspoken critic of President Vladimir Putin, became sick aboard an airplane while on a lecture tour in 2019; he spent five days in a coma.

Doctors attributed the illness to bacterial food poisoning. But the illness and circumstances bore strong resemblance to the case of Navalny, who last year fell sick aboard a domestic flight and was hospitalized in a coma before being transferred to Germany for treatment, where doctors said he had been poisoned with a Soviet-developed nerve agent Novichok.

Bellingcat, an Amsterdam-based international organization that focuses on open-source investigations, identified what it said were several alleged agents of Russia's Federal Security Service who had trailed Navalny directly before his poisoning. In a report Wednesday, it said cellular phone records and airline ticket purchases showed that two of these agents had traveled to the same cities as Bykov and at the same time.

Navalny spent five months in Germany recuperating from the poisoning. He was arrested upon his return to Russia in January and subsequently ordered to spend 2 1/2 years in prison on the grounds that his convalescence in Germany violated a suspended sentence that had been handed in an embezzlement conviction.