Russia has jailed the killer of opposition leader Boris Nemtsov for 20 years, and handed four accomplices in the 2015 murder sentences ranging from 11 to 19 years.

Last month, the five men were found guilty of killing Mr Nemtsov in 2015.

But the late politician's allies said the investigation had been a cover-up and that the people who had ordered his killing remained at large.

Thousands march in Moscow to remember murdered opposition leader Nemtsov

Mr Nemtsov was walking with his girlfriend across the Bolshoy Moskovoretsky Bridge near the Kremlin when he was shot four times in the back with a pistol on 27 February, 2015.

His killer then sped off in a getaway car and Mr Nemtsov was pronounced dead at the scene.

Putin critic: Boris Nemtsov took a leading role in the opposition to the Kremlin’s policies (EPA)

Prosecutors had asked for Zaur Dadayev to be sentenced to life and it was not immediately clear why the judge chose the shorter term.

Dadayev was an officer in the security forces of Chechnya's leader Ramzan Kadyrov and allies have criticised investigators for not studying a possible role of Mr Kadyrov in the killing.

The other four Chechen men convicted of being Dadayev's accomplices received jail sentences ranging from 11 to 19 years.

"The shortcoming of this sentencing is that those who ordered and organised this crime are not in the dock," said Vadim Prokhorov, a lawyer for Nemtsov's daughter Zhanna.

State prosecutors said the group had followed Mr Nemtsov around the Russian capital and had been promised a bounty of 15 million roubles (£193,000) between them for the high-profile assassination.

Shamsudin Tsakayev, Dadayev's lawyer, told Reuters after the sentencing that there was "incontrovertible proof" that his client had not committed the crime.

In pictures: Marchers mourn Boris Nemtsov in Moscow Show all 7 1 /7 In pictures: Marchers mourn Boris Nemtsov in Moscow In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march People march in Moscow in memory of opposition leader Boris Nemtsov (Dmitry Lovetsky/AP) In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march A man prepares portraits of opposition leader Boris Nemtsov who was gunned down on Friday (AP/Pavel Golovkin) AP/Pavel Golovkin In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march People hold posters of Kremlin critic Boris Nemtsov, who was shot dead on Friday night, during a march to commemorate him in central Moscow (SERGEI KARPUKHIN/Reuters) (SERGEI KARPUKHIN/Reuters) In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march Riot police near the site of Russian opposition veteran leader Boris Nemtsov killing in central Moscow (SERGEI ILNITSKY/EPA) SERGEI ILNITSKY/EPA In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march People hold flags and posters during a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow (MAXIM SHEMETOV/Reuters) MAXIM SHEMETOV/Reuters In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march Portraits of murdered Russian opposition veteran leader Boris Nemtsov are held by members of the crowd (EPA/SERGEI ILNITSKY) In pictures: Marchers mourn Boris Nemtsov in Moscow Russian protest march People march in memory of opposition leader Boris Nemtsov (Pavel Golovkin/AP) AP

Mr Nemtsov was a top opponent of President Vladimir Putin and the killing sent shockwaves through Russia's beleaguered opposition supporters.

Hours before his death, Mr Nemtsov denounced Vladimir Putin's policies as “mad, aggressive and deadly” and was scheduled to lead an anti-government Spring March protesting against the Kremlin’s alleged involvement in the violence in Ukraine.

He was also working on a report containing evidence he believed would prove Russia’s direct involvement in the separatist rebellion that has raged in eastern Ukraine since April 2014. Moscow has continually denied accusations it is supporting the rebels with troops and sophisticated weaponry.