Yashin rejected suggestions radical Islamists were behind the murder of Boris Nemtsov

A close ally of the murdered Russian opposition politician, Boris Nemtsov, says he is "totally sceptical" that the two men charged are his killers.

Ilya Yashin spoke to the BBC after Zaur Dadayev and Anzor Gubashev, both of Chechen origin, were charged with his murder and three other men were arrested.

Mr Yashin rejected suggestions radical Islamists were behind the murder.

He believed those behind the killing were in Russia, and even in government.

On Sunday a court in Moscow charged Zaur Dadayev and Anzor Gubashev with shooting Mr Nemtsov on a bridge near the Kremlin on 27 January. Mr Dadayev had admitted his involvement, the court said.

Three other suspects were remanded in custody. A sixth man is reported to have killed himself in a standoff with police in the Chechen capital Grozny.

Chechen leader Ramzan Kadyrov described Mr Daedayev as a devout Muslim who was shocked by cartoons of the Prophet Muhammad published by the French satirical magazine Charlie Hebdo.

Russian investigators have previously said they were looking into the possibility that Mr Nemtsov was killed over his defence of the publication.

But Mr Yashin said Mr Nemtsov had not been a prominent critic of Muslim radicalism and had concentrated his attacks on President Vladimir Putin and his government.

He said he did not believe Mr Nemtsov's killers were from outside Russia, calling his murder "an act of terror to scare society".

"I believe that the organisers of the murder are in Russia and I believe that they are in the Russian government," he added.

He said it was very important that the organisers of the murder were caught, because if they remained free Mr Nemtsov's murder might not be the last.

The location of the murder, right next to the Kremlin, made him think that the killers could not have acted without support from the authorities, he said.

He therefore believed that those people criticised by Mr Nemtsov in recent years should be under investigation.

The three suspects remanded in custody are Mr Gubashev's younger brother, Shagid Gubashev, and two men named as Ramzan Bakhayev and Tamerlan Eskerkhanov. Reports say all three have denied any involvement in the murder.

Four of the five men in custody are from the northern Caucasus region and were detained in the republic of Ingushetia which borders Chechnya, Russian media say.

The Russian Investigations Committee is treating the case as a "contract killing", Interfax news agency reported.

According to the sections of the criminal code cited in court, investigators believe the murder was carried out by a group of people, that it was committed on contract for financial gains, and that it also involved extortion and banditry, Interfax says.

President Vladimir Putin has condemned Mr Nemtsov's murder and called for an end to "shameful" political killings in Russia.

But leading opposition figure Alexei Navalny has accused the Kremlin of ordering the assassination to cow the opposition amid Russia's mounting economic problems.

Mr Nemtsov was killed days before a march he had been organising against the conflict in Ukraine.

He had also been drafting a report expected to expose covert Russian military involvement in the conflict.