The two men arrested over the murder of opposition politician Boris Nemtsov could have carried it out, the Investigative Committee of Russia has said.

A statement [RU] on its website follows the official report that two Russian citizens from the Caucasus were arrested over their alleged involvement in what Russian authorities suggest might have been "a contract killing".

"According to data from the investigation, the detained are involved in the organization and execution of the murder," Vladimir Markin, who represents the investigative body, has announced.

Ylya Yashin, one of Nemtsov's closest collaborators in the late leader's RPR-PARNAS party, told Interfax he welcomed the developments.

"We hope that... this is not a mistake, but a result of good work of law enforcement agencies," Yashin is quoted as explaining, but adds more details are needed if one is to have a clearer picture.