Men place candles as they arrive to attend a farewell ceremony to the slain opposition leader Boris Nemtsov in Moscow on Tuesday. Russia has vowed to find the killers of Nemtsov as fresh details emerged about the most shocking political assassination during Vladimir Putin’s rule.

AFP/Moscow

Thousands of mourners on Tuesday filed past the coffin of slain Russian opposition leader Boris Nemtsov, bidding farewell to a charismatic activist whose brazen assassination shocked the country.

The 55-year-old former deputy prime minister, longtime critic of President Vladimir Putin and anti-corruption crusader who was gunned down outside of the Kremlin walls late on Friday, will be buried in Moscow later on Tuesday.

The most shocking political murder of Putin's rule sent shockwaves across Russia and triggered international condemnation led by US President Barack Obama.

Former British prime minister John Major was among the first to arrive at the Andrei Sakharov rights centre in central Moscow early on Tuesday, where Nemtsov's body lay in state.

The slain politician's mother, Dina Eidman, who turned 87 on Tuesday, arrived wearing a black headscarf.

Russian Deputy Prime Minister Arkady Dvorkovich carried a bouquet of red roses as he walked in, as did former prime minister Mikhail Kasyanov, himself now an opposition leader.

Putin was not due to attend the funeral, with the Kremlin sending a low-level official instead.

'Ashamed of our country'

"We came because we feel ashamed of our country, of our people, that we let such a thing happen. It's our cruelty, our fear," said one of the mourners, Dmitry Afanasyev. "Putin is to blame. But we are too."

"It's a shock. It's the system that killed him," said another mourner, Vladimir Shlamin. "We are against the system that kills great people."

Bach played in the background as well-wishers came up to the coffin to lay flowers, many crossing themselves.

Polish Deputy Foreign Minister Konrad Pawlik was also set to attend as well as Lithuanian Foreign Minister Linas Linkevicius.

But several senior officials from Poland and Latvia said Monday they had been denied entry into Russia to attend the funeral in retaliation for EU sanctions over Ukraine.

Polish Senate speaker Bogdan Borusewicz was refused entry by Moscow, the Polish foreign ministry said.

Latvian MEP Sandra Kalniete said she had also been refused entry into Russia at Moscow's Sheremetyevo airport, but was not given a reasonable explanation for the ban.

Nemtsov was gunned down shortly before midnight on Friday while walking across a bridge just a short distance from the Kremlin with his Ukrainian model girlfriend Ganna Duritska.

Putin, whose rule has seen the steady suppression of independent media, opposition political parties and independent-minded business figures, called the murder a "contract killing" and said it was a provocation.

He promised an all-out effort to catch the perpetrators.

Girlfriend returns to Kiev  

Investigators said on Tuesday they had examined security camera footage and questioned witnesses and were going to carry out a number of forensic tests.

A reward of 3mn roubles ($48,000) was offered for information on Nemtsov's death, a substantial amount in Moscow, where the average monthly salary is 60,000 roubles ($960).

Late Monday 23-year-old Duritska - the chief witness in the murder - was allowed to return to Kiev.

She said she had given all the information she could to investigators and did not plan to attend the funeral.

Speaking via a fuzzy Skype connection from a Moscow apartment, Duritska said earlier she did not see where the assassin came from. But she did notice a light-coloured car quickly drive off, she said.

She said she was immediately taken in for questioning which lasted through the night.

Investigators on Tuesday said that Duritska was a key witness and "could know some circumstances that have significance."

After the ouster of Ukraine's Kremlin-backed president Viktor Yanukovych ties between Moscow and Kiev were plunged into crisis, as Moscow seized Crimea and a pro-Russian insurgency erupted in Ukraine's east.

Friends of Nemtsov said he had been working on a report containing what he described as proof of secret Russian military involvement in the bloody uprising by pro-Moscow militias in eastern Ukraine.

He had also spoken of his fear of being killed in Russia, where a string of other prominent opposition figures have been murdered since Putin came to power 15 years ago.

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