Russian authorities have released Russian investigative journalist Ivan Golunov and dropped all charges only days after his arrest on multiple drug counts and hospitalization with injuries purportedly inflicted by police.

The dramatic reversal, announced by Interior Minister Vladimir Kolokoltsev, came amid a nationwide campaign on Golunov's behalf, including journalists and others picketing Moscow police headquarters for five days.

More than 400 people, including journalists, were detained Wednesday during an unauthorized pro-Golunov march in central Moscow by around 1,200 people, according to the privately held Russian news agency Interfax.

Among those detained was Alexei Navalny, President Vladimir Putin’s most prominent political foe.

One woman even showed up at Kremlin reception wearing a T-shirt "I / we are Ivan Golunov," the Russian newspaper Novaya Gazeta reported.

“We should not stand down, even if Ivan is free. There are a number of other people in his situation in this country,” said Maxim Reznik, a member of the St. Petersburg City Council who attended a smaller demonstration Wednesday in that city.

Kolokoltsev said Tuesday that the journalist was freed because of lack of evidence.

“I believe that the rights of any citizen, whatever his professional affiliation, ought to be protected,” the minister said, adding that he would ask Putin to dismiss two police generals, including the drug chief of the Moscow police, and suspend the officers who detained the journalist.

In an unusual development, Golunov's release was covered live on on a state-controlled 24-hour news channel.

“I still can’t believe in my release,” a tearful Golunov said as he was met by cheering journalists and supporters. “I need some time to get my breath back.”

The 36-year-old reporter for the Latvia-based news site Meduza has long been a thorn in the side of Russia's power center after repeatedly exposing corruption among business people and political figures, as well as uncovering fraudulent financial schemes in Moscow.

He insisted his arrest would not deter his journalistic work. “I will keep doing investigations to justify the trust of all those who supported me,” he said.

Golunov, who was arrested last week, said he hopes police will stop trying to frame innocent people, adding: “I hope it will not happen to anyone else in our country.”

He had alleged police planted the drugs on him, faced up to 20 years in prison.

Meduza said on its website that Golunov had been beaten after his arrest and was being "being persecuted because of his journalistic activity."

Meduza credited the release to a strong backlash among Russian journalists backed by international groups, as well public protests in several Russian cities.

"This is the result of an unprecedented international solidarity campaign among both journalists and their allies. Together, we made the unbelievable happen: We stopped the criminal prosecution of an innocent man.

Meduza said Golunov had received threats in recent months over a story he was working on.

Police had initially released photos that they said showed drug paraphernalia in his apartment, but these were later withdrawn, BBC Russian journalist Olga Ivshina reported.

The police, she adds, admitted that "most of the published photos had not been taken at Mr Golunov's flat after all, but were related to another criminal investigation that might be linked to his detention."

The head of human rights organization Agora, Pavel Chikov, told Russian news agencies the reporter was suspected of having a concussion and a broken rib. In a video taken after his arrest and posted by the Russian news site Breaking Mash, Golunov showed marks on his back.

PEN America, which advocates for free expression worldwide, said in a statement that the "questionable accusations"against the journalist "reflect the Russian government's long-standing practice of harassing its critics via both legalistic and clearly extra-legal means, which appear to have widened as regional elections are coming in September."

Michael McFaul, former U.S. ambassador to Moscow during the Obama administration, said Golunov's arrest reflects the brutality of the Putin era.

"Putin's regime is an autocracy," he said on Twitter."Whether Putin personally orders every assault on human rights or rule of law is immaterial. This is his regime."

Contributing: Associated Press