Russian authorities have charged two men in connection with the murder of Kremlin critic Boris Nemtsov, including a former police officer from Chechnya who confessed to his involvement in the killing, officials said.

Five men faced a Moscow court including former policeman Zaur Dadayev and fellow Chechen Anzor Gubashev, who were both charged with killing Mr Nemtsov who was shot four times on February 27.

Officials said a sixth suspect threw a grenade at police who came to arrest him in the Chechen capital and killed himself with another grenade.

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The men are all from the volatile northern Caucasus region where Russia has fought two devastating wars against Chechen rebels and where security forces continue to clash with Islamist insurgents.

But the investigation has been met with profound distrust by many in Russia who believe the Kremlin had the most to gain from Mr Nemtsov’s death.

Russian President Vladimir Putin. Photo: AAP

President Vladimir Putin has condemned the murder and called for an end to “shameful” political killings in Russia.

Mr Nemtsov was shot dead while walking with his girlfriend along a bridge outside the Kremlin in a brazen assassination that has sent shivers through the country’s opposition.

Heavily armed police marched the five handcuffed suspects through hallways packed with journalists and into two separate courtrooms where they were placed inside defendants’ cages and ordered to be held for around two months pending the investigation.

According to documents read out in court, the accused are charged under a section of the Russian criminal code which shows investigators believe the murder was carried out by a group of people for financial gain, the Interfax news agency reported.

The charges also involve extortion and banditry. Investigators said they were still seeking others who may have been involved.

However, as in a string of other killings of Russian opposition figures, officials have yet to shed light on who might have ordered the late-night murder of the 55-year-old Nemtsov, a fierce critic of Mr Putin.

Dadayev, a decorated former deputy commander in a Chechen police unit born in 1982, and Gubashev, 31, who worked for a private security company in Moscow, were arrested on Saturday in the province of Ingushetia which neighbours Chechnya.

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They were both charged with murder but Gubashev denied involvement.

“The participation of Dadayev is confirmed by his confession,” said presiding judge Nataliya Mushnikova, according to state news agencies.

Court spokeswoman Anna Fadeyeva told the RIA Novosti news agency that the other three men were only considered suspects at this stage.

They are Gubashev’s younger brother Shagid, Ramzat Bakhayev, 45, and Tamerlan Eskerkhanov, 34.

“The suspects denied their involvement in this crime but investigators have proof of their involvement,” a representative for the probe told the court.

Killing politically motivated: Nemtsov’s daughter

However no information emerged as to the possible motive the men could have had in killing the former prime minister turned charismatic opposition leader.

Mr Nemtsov’s allies believe his assassination was a hit ordered by the top levels of government determined to silence dissenters. The allegation has been strenuously denied.

The slain leader’s daughter, Zhanna Nemtsova, said in an interview with CNN from Germany that the murder was obviously “politically motivated”.

“I think that now Russia has crossed the line after this murder, and people will be frightened to express their ideas which contradict … the official standpoint.”

Her comments echo those heard from Kremlin critics such as activist Alexei Navalny, who accused “the country’s political leadership” of ordering a hit on Mr Nemtsov.

Mr Nemtsov, who had long complained of being followed and having his phone tapped, had spoken of his fear of being killed.

Mr Putin has described his killing as a tragedy that brought disgrace on Russia and vowed that everything would be done to bring to justice those who committed a “vile and cynical murder”.

– ABC