Russian police have arrested another two men over the killing of opposition activist Boris Nemtsov, who was gunned down in the center of Moscow, state media reported Sunday, bringing the number held to four.

Russian police have arrested another two men over the killing of opposition activist Boris Nemtsov, who was gunned down in the center of Moscow, state media reported Sunday, bringing the number held to four.
  
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 neighboring 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 spokeswoman 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 Nemtsov was shot four times in the back as he strolled along a bridge in the heart of the capital.