A prominent Russian investigative journalist who was detained this week for alleged drug offences has been placed under house arrest.

Key points: Police said that Ivan Golunov was found with four grams of a synthetic drug

Police said that Ivan Golunov was found with four grams of a synthetic drug Journalists instead believe his arrest was in direct retribution for his investigative work

Journalists instead believe his arrest was in direct retribution for his investigative work Human rights group Agora said Mr Golunov may have concussion and a broken rib

Ivan Golunov was taken to a Moscow court late Saturday after undergoing medical examination that was initiated when he complained of feeling poorly in police custody.

He left the courtroom after the ruling to place him under house arrest until 7 August.

In the court hearing, he denied being involved with drugs and said he would be willing to help investigators.

While speaking to journalists from the cage in which defendants are held in Russian courtrooms, Golunov broke into tears.

Ivan Golunov, 36, was on his way to a meeting with a source on Thursday when he was taken into custody in central Moscow and where illegal drugs were found in his rucksack, according to police and his employer, the online news portal Meduza.

A lawyer for Golunov, who is known for investigating alleged corruption among Moscow city officials, said he believed police had planted the drugs on his client to frame him and that Golunov had been physically beaten.

In the court hearing, he denied being involved with drugs and said he would be willing to help investigators. ( AP: Dmitry Serebryakov/ Moscow )

"The detainee … complained of feeling unwell. An ambulance was called … the ambulance doctors decided that he should be taken to a hospital for examination," Interfax quoted a Moscow police press office as saying.

The head of human rights organisation Agora, Pavel Chikov, told Russian news agencies Golunov was thought to have a concussion and a broken rib.

Police are alleging four grams of a synthetic stimulant were found in his backpack. But many journalists suspect the arrest was retribution for Golunov's investigative work.

The editorial management of Meduza, which is based in Latvia, said in a statement that Golunov had received threats in recent months in connection with a story he was working on.

Reuters/AP