ST. PETERSBURG — A prominent Russian investigative journalist was detained on drug-related allegations, his editors said Friday, in a case that his supporters described as fabricated and that had the potential to augur a new, more dangerous phase for journalists working in Russia.

The journalist for online news outlet Meduza, Ivan Golunov, was taken into custody in central ­Moscow on Thursday after police searched him and found five packets of mephedrone, the authorities said. More of the illegal drug, as well as a scale, were found in Golunov’s apartment, the police said.

Golunov managed to let friends know that the drugs were planted, Meduza said in a statement

“We are convinced that Ivan Golunov is innocent,” said the statement by Meduza chief executive Galina Timchenko and editor in chief Ivan Kolpakov. “Moreover, we have reason to believe he’s been targeted because of his work as a journalist.”

Independent journalists in Russia often deal with threats and harassment, but arrests of prominent reporters in Moscow — even critical ones — are rare. Despite the Kremlin’s control of the television airwaves, Russian journalists often publish splashy investigative reports spotlighting government corruption via a fast-
evolving panoply of online news start-ups.

“Pressing drug charges against inconvenient voices is nothing new in today’s Russia,” wrote Tanya Lokshina, Europe and Central Asia associate director at Human Rights Watch. “But Golunov’s case is the first time it’s been done to a journalist from a high-profile media outlet.”

Working for the Russian-language outlet Meduza, which is based in Latvia, Golunov wrote about predatory microfinance, corruption at Moscow City Hall, and shady dealings in the funeral industry. 

“The number of people whose interests were affected by Golunov’s articles — both business executives and officials — is likely in the hundreds,” the newspaper Vedomosti said in a commentary on the arrest. 

Golunov was beaten in detention and at first denied access to a lawyer, Meduza reported. The Moscow police denied that he was beaten and said proper procedures were followed in giving him access to a lawyer. Moscow Police Chief Oleg Baranov has taken the case under his personal supervision, the police said.

One by one, journalists and other backers of Golunov stood before the Moscow police headquarters and held up signs of support Friday. The one-person protests were meant to avoid detention by police.

“We call on our colleagues and our readers not to stay silent,” said an editorial by Mediazona, a rival online news outlet. “We must defend Ivan for the future of independent journalism in Russia, without which the whole country has no future.”