Updated

A newspaper editor on Wednesday accused Russia's top investigator of threatening to kill one of his journalists following a dispute over coverage.

Dmitry Muratov, the editor of Novaya Gazeta, which employed journalist Anna Politkovskaya until her murder in 2006, urged Investigative Committee chief Alexander Bastrykin to provide security guarantees for Sergei Sokolov.

Muratov claimed in an open letter that on June 4 Bastrykin's guards forcibly placed Sokolov into a car and drove him to a forest — once there, he alleged, their chief got into the car and threatened to kill him.

The Investigative Committee would not comment on the letter, which dominated Russian online media and social networks Wednesday.

Muratov claims that Bastrykin was angered by a June 4 article by Sokolov that accused him of failing to punish the perpetrators of a 2010 killing of 12 people, including four children, by a gang in southern Russia.

"The cruel truth is that you rudely threatened my deputy's life in a fit of anger," Muratov wrote. "And you even joked that you will then investigate the case yourself."

He said Sokolov had left Russia following the threat.

Vladimir Varfolomeyev, one of five Russian journalists who picketed the Committee building in northeast Moscow to protest Bastrykin's alleged threat to Sokolov, tweeted Wednesday that they have all been detained.

Novaya Gazeta's investigations into official corruption and its harsh criticism of the Kremlin have put its journalists in the line of fire. Four of its reporters have been killed since 2000, including Politkovskaya, a fierce critic of the Kremlin and its policies in Chechnya who was gunned down in the elevator of her Moscow apartment building in October 2006. Others have been harassed and attacked.

The murders and attacks on journalists haven't been solved.

"We treated your words in all seriousness," Muratov said. "We have covered many wars and have buried our colleagues."

He said he had posted a copy of the letter to Bastrykin after he refused a proposal to meet with Novaya's editorial board and discuss the issue.

Founded in 1993, Novaya Gazeta is published three times a week and has a circulation of about 200,000. Business magnate Alexander Lebedev and former Soviet leader Mikhail Gorbachev own a 49 percent stake, while the remaining shares are controlled by Novaya's staffers.