Investigative reporter Ivan Golunov, probing corruption in the funeral industry and food markets, was arrested last week before being placed under house arrest over allegations that he manufactured and dealt drugs.
The Kremlin said on Monday it was carefully monitoring the case of detained reporter Ivan Golunov and admitted it threw up a "great number of questions."
President Vladimir Putin's spokesman Dmitry Peskov, however, defended the law-enforcement system in general, saying people make mistakes in separate cases.
"We are carefully monitoring how this case is developing," Peskov told reporters. "This concrete case has triggered a great number of questions."
Golunov, who works for the independent website Meduza, was beaten and kept in custody for 12 hours without a lawyer after he was stopped by police in Moscow on Thursday, according to his lawyer.
He was transferred to house arrest on Saturday following a public outpouring of support, but he still faces drug dealing charges that could send him to prison for up to 20 years.
For the first time in their history, three Russian newspapers will print identical above-the-fold designs on their front pages. They read "I/WE ARE IVAN GOLUNOV." pic.twitter.com/FCuEY2LEIv— Meduza in English (@meduza_en) June 9, 2019
The 36-year-old investigative reporter was arrested last week over allegations that he manufactured and dealt drugs.
He could face up to 20 years in prison if convicted.
His defence and supporters say the drugs had been planted on him to punish him for his investigations.
Golunov's prompted an unprecedented show of solidarity among Russian journalists, with three top dailies publishing the same front page on Monday.
Kommersant, Vedomosti, and RBK among the most respected daily newspapers in the country, published a joint editorial under the headline "I am/We are Ivan Golunov," calling for a transparent probe into the case.
The papers dismissed the evidence presented in the case against the journalist.
Observers say Golunov's case has put the Kremlin in an uncomfortable situation, forcing the authorities to either side with law-enforcement agencies or the journalist's supporters.
Probing funeral business
Golunov rose to prominence with his investigations into corruption at the Moscow City Hall, the crime-ridden funeral industry and the murky food markets.
The journalist told the court on Saturday that he has received threats related to his investigation into Moscow's funeral business.
Meduza's director general Galina Timchenko said on the Ekho Moskvy radio station on Monday that Golunov told her in March about the threats after his piece came out.
Timchenko said she had spoken with Golunov about security measures but she could not get Golunov to leave the country.
Does Russian state tv’s main weekly news show reflect on the widespread shock & anger of Russian journalists over the detention of investigative reporter Ivan Golunov? No. But it does show a state tv correspondent interviewing a Chinese panda. Different priorities... pic.twitter.com/hIQtGhd6ym— Steve Rosenberg (@BBCSteveR) June 9, 2019
Asked to comment on the widespread lack of trust in the work of law-enforcement agencies, Putin's spokesman Peskov sought to defend it.
"I believe it would be wrong to make general conclusions about the mistrust towards the entire system based on his case," he said.
But Peskov said mistakes can happen.
"People work everywhere," he said. "The most important thing is to admit mistakes and explain how they happened and no longer repeat them."
He expressed hope that the General Prosecutor's Office would look into whether the police committed violations during Golunov's detention.