The daughter of the murdered Russian opposition leader, Boris Nemtsov, has accused Vladimir Putin of being “politically responsible” for her father’s death.

Zhanna Nemtsova said that the motive for the killing was related to her father’s role over the last decade as, in her words, the most prominent critic of the president.

“He was the most powerful leader of the opposition in Russia,” she said in an interview conducted in Italy with BBC Newsnight.

“After his death the opposition is beheaded and everybody is frightened. People and politicians … both of them.”

Nemtsov was killed by four shots to the back on 27 February as he walked across a bridge next to the Kremlin, in central Moscow.

His daughter, a business journalist normally based in Moscow, was said to have not previously regarded herself as an activist, but she conceded that the way in which she was viewed, in some quarters at least, was now likely to change.

“I think that after I have expressed my opinion on the murder I think that authorities in Russia could regard me as a political activist,” she said, adding that she was not afraid to return to Russia and planned to do so this weekend.

“I am not afraid. I will go back on 15 March but I said they have killed my father. I cannot just keep silent. It’s absolutely impossible.”

Asked if she believed that Putin had issued an order for her father to be killed, she replied: “I don’t have evidence but politically he is responsible.”

Nemtsova said that her father had been under pressure for the last decade, adding: “He tried to resist … there was a lot of stress but he was a fighter.”

Father and daughter had talked about the possibility of him being jailed but she said that he had never mentioned to her that there could be a “substantial threat” to his life.

At the time of his death, he was said to have been working on a report detailing Russia’s military involvement in eastern Ukraine, something which he had discussed with her.

“Officially, technically, Russian troops are not involved in the military conflict in Ukraine but what they actually do is that these soldiers resign from the army and then they go there by order,” she said.

A former law enforcement officer charged with involvement in the murder of Nemtsov said on Wednesday that he was forced into his confession to the killing.

Zaur Dadayev, who was the deputy commander of the north interior ministry battalion in Russia’s restive Chechnya republic, was detained in neighbouring Ingushetia and charged with the murder in Moscow this weekend.