Thousands of people have marched through the centre of Moscow in an anti-government protest marking two years since opposition leader Boris Nemtsov was gunned down near the Kremlin walls.

The crowds were reportedly shouting slogans including “Russia will be free” and “Putin is war.”

Mr Nemtsov a 55-year-old former deputy prime minister and prominent critic of Russian president Vladimir Putin was shot dead on a bridge near the Kremlin late in the evening of February 27-02-2015.

He was shot in the back several times as he walked home from a restaurant with his girlfriend.

The apparent contract killing sparked outrage and fear among Russia's beleaguered opposition – which has been struggling to deal with pressure from the Kremlin, the flight abroad of leading activists and political infighting over recent years.

People gather in memory of opposition leader Boris Nemtsov, portrait centre, in St. Petersburg, Russia, 26-02-2017. Image: AP Photo/Dmitri Lovetsky

Organisers of yesterday’s march said just over 15,000 people took part, calling for further investigations into the killing.

The attendance at Sunday's rally was significantly lower than a year ago, when organizers estimated almost 25,000 people joined a Nemtsov memorial march.

Russian authorities have charged several Chechen men with the murder, but lawyers for Mr Nemtsov's daughter said the investigation had failed to uncover who ordered the shooting.

Mr Nemtsov's family and friends have claimed the murder was a political hit with a trail that leads to senior Chechen officials who have never been charged or questioned.

"We gathered here to demand bringing of Boris Nemtsov's killers to justice, not only its performers but also its organizers and those who ordered it," Ilya Yashin, a Russian opposition activist and an organizer of the march, told Reuters.

"We gathered here to demand political reforms and release of political prisoners."

The authorities blocked off several streets in central Moscow for Sunday's event, sealing in the marchers with metal fencing guarded by police.

Before he was killed, Mr Nemtsov had authored a damning report on Putin's rule and had been working to expose the Russian military's role in Ukraine.

A number of other demonstrations took place in other cities around the country including in St Petersburg and in Mr Nemtsov’s hometown of Nizhny Novgorod yesterday.

Thousands of flowers were laid on the bridge where he was shot.