Russia detains two men over shooting of outspoken Vladimir Putin critic Boris Nemtsov

Russia's head of internal security told state TV that two men had been detained in relation to the murder

Protesters take to the streets in the days following Boris Nemtsov's murder (AFP)

Two men have reportedly been detained for the murder of outspoken Putin critic Boris Nemtsov.

Anzor Gubashev and Zaur Dadaev are being held in relation to Mr Nemtsov’s murder last Friday, the head of Russia’s federal security service (FSB) Alexander Bortnikov told state TV news channel Rossiya-24.

Russia Today reported that the men are believed to come from Russia's southern region of the North Caucasus, a political uneasy region that includes constituent republics such as Chechnya.

Mr Bortnikov said they "were suspected of carrying out this crime," but did not offer further details on the men and it remains unclear if either of the suspects was believed to have fired the four shots that killed Mr Nemtsov.

It is alleged that the car used by the suspects has been found and was used to identify the two men, a source familiar with the investigation told Russia's Interfax news agency, the BBC reported.

The 55-year-old vocal critic of Russian president Vladimir Putin was walking over Moskvoretsky Bridge with his Ukrainian girlfriend Anna Duritskaya when he was shot dead just before midnight on 27 February.

Mr Nemtsov’s death – within sight of the Kremlin – provoked international criticism, with world leaders calling for a swift and thorough investigation into his murder.

President Putin has publicly condemned the murder, labelling it a "provocation", and calling for an end to "shameful" political killings.

Russian investigators are allegedly pursuing a number of inquiries into the murder, including the possibility that Mr Nemtsov's death was an attempt to smear the Russian president's image. It also claimed it was looking into the option the murder was in connection to possible Islamic extremism and the former deputy prime minister's personal life.

However, opposition members have claimed that the Kremlin ordered the killing in retaliation for Mr Nemtsov's sustained criticism of Mr Putin's foreign policies, particularly the Kremlin's alleged involvement in the Ukrainian conflict.

Additional reporting by Associated Press and Reuters