The daughter of Russian opposition politician Boris Nemtsov said that President Vladimir Putin is "politically" responsible for her father's death.

In an interview in Italy with the UK-based BBC news channel on Wednesday, Zhanna Nemtsova said that her father was "a critic of Putin, he fought with Putin, with nobody else," and said she blamed the president for his death.

"After his death the opposition is beheaded and everybody is frightened," she said.

The killing of the 55-year-old Nemtsov, who was shot dead near the Kremlin in late February, has infuriated the opposition, which sees Putin as responsible for his death.

The shooting of Nemtsov, a former deputy prime minister, was the highest-profile killing of an opposition leader during Putin's 15 years in charge.

Five people have been detained and two of them charged for carrying out the killing, though Nemtsov's colleagues worry that whoever ordered his murder may not be found.

A former Chechen police officer who admitted to taking part in the murder had "likely confessed under torture", a member of the Kremlin's human rights council has said.

Zaur Dadayev allegedly confessed and was charged, but has now insisted to the council's Andrei Babushkin that he is "innocent" and only made the admission under duress.

"There are reasons that lead us to believe Zaur Dadayev confessed under torture," Babushkin told the AFP news agency on Wednesday, after a visit to the suspect's Moscow prison cell.

Dadayev, who was arrested in North Caucasus region of Ingushetia last week, was charged by a Moscow court on Sunday with the murder alongside Anzor Gubashev, who worked for a private security company. The two men and three other suspects were remanded in custody.

Dadayev alleged that he spent two days manacled and with a sack over his head.