MOSCOW (AFP) - The Russian police have arrested another two men over the killing of opposition activist Boris Nemtsov, who was gunned down in the centre of Moscow, state media reported on Sunday, bringing the number held to four.
Mr Albert Barakhoyev, secretary of the Security Council of Russian republic of Ingushetia told state news agency RIA Novosti that the pair had been taken into custody over the assassination of the 55-year-old former prime minister.
Both of the men, arrested in Ingushetia, are from neighbouring Chechnya in the volatile northern Caucasus. One of them is the younger brother of Anzor Gubashev, whose arrest alongside Zaur Dadayev was announced by Russian security officials on Saturday.
RIA Novosti reported that Dadayev was a deputy commander for a battalion attached to the Chechen interior ministry while Gubashev worked for a private security company in Moscow.
The suspects were due to appear in court in central Moscow on Sunday, where security had been stepped up, to determine whether to extend their detention, a spokesman for the court Anna Fadayeva told the news agency. However it was not clear if all four men would be appearing.
The arrests come a little over a week after Mr Nemtsov, a longtime critic of President Vladimir Putin, was shot four times in the back as he strolled with his girlfriend along a bridge in the heart of the capital, in full view of the Kremlin and tourist sites such as Red Square.
However no information has emerged as to the possible motive the men could have had in killing the charismatic opposition leader. His 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 brazen assassination sent shockwaves through the country's opposition and prompted an outpouring of international condemnation.
Investigators have suggested the killers wanted to destabilise Russia, which is facing its worst stand-off with the West since the Cold War over Ukraine.
But they were also probing the possibility he was assassinated for criticising Russia's role in the Ukraine conflict or his condemnation of January's killings at the Charlie Hebdo satirical weekly in Paris by Islamist gunmen.