Several EU politicians and Russia’s opposition leader have been barred from attending the funeral of murdered Russian politician Boris Nemtsov.
A Polish politician was denied a visa under existing Russian sanctions while a Latvian MEP was turned back after arriving at a Moscow airport.
Opposition leader Alexei Navalny was denied permission to leave jail, where he is serving a 15-day sentence.
Mourners are filing past Nemtsov’s coffin at Moscow’s Sakharov centre.
His funeral will be held in the afternoon (local time) at a Moscow cemetery, Troyekurovskoye, where murdered journalist Anna Politkovskayta was buried in 2006.
Nemtsov, a fierce critic of President Vladimir Putin, was killed on a bridge near the Kremlin wall on Friday night.
No arrests have been made and no clear motive has been established for the crime.
New CCTV footage of the presumed getaway car has been released by a pro-Kremlin Russian news website, LifeNews. The video shows a vehicle making its way along Moscow streets but there is no close-up on the suspects inside.
Friends and supporters of Boris Nemtsov are gathering in Moscow to say their final farewells. As they file past his coffin, the crowds will remember a man who was full of energy and life, who burst on to the political scene in the 1990s as a young reformer, who believed passionately in democracy. He was never afraid to speak his mind, to campaign and to criticise.
In recent years he had been a fierce opponent of President Putin, exposing corruption and speaking out against the war in Ukraine.
Boris Nemtsov was shot dead – with four bullets to the back – just beside the Kremlin. It should be one of the most secure spots in the country but more than three days on, police still do not have a suspect, the murder weapon or even the getaway car.
There is nothing to explain for sure why Nemtsov was killed and why, so demonstratively, right in the heart of Russia’s capital.
Former UK Prime Minister John Major, who was in Moscow to pay his respects, called for a full, transparent investigation into Nemtsov’s murder, saying his voice would not be silenced.
It was, he added, his “saddest ever visit to Moscow”.
Latvian MEP Sandra Kalniete told the BBC she had been refused entry into Russia at Sheremetyevo airport in Moscow without a proper explanation.
Ms Kalniete said she had been made to wait two hours at the airport before being denied entry.
“I was not coming to Russia to make political declarations and standing on the corner to offend the people,” she said.
“I was going to Russia to pay tribute to Boris Nemtsov, who I consider one of the brightest and most admirable political personalities in Russia.”
Bogdan Borusewicz, the Polish senate speaker who was to have led a delegation from his country, was denied a visa.
Russia said he was on a list of Polish officials barred from travelling to Russia, drawn up after the EU imposed sanctions on Russia over its involvement in Ukraine.
President Putin will not attending the funeral, the Kremlin said, but will send a representative in his place.
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Mr Navalny is currently in custody for 15 days for handing out leaflets publicising a demonstration.
He appealed against a court decision not to release him temporarily but the appeal is only going to be heard on Wednesday, the day after the funeral.
Tens of thousands of people marched through central Moscow on Sunday to honour Nemtsov, with the opposition claiming some 50,000 people had attended the event.
Nemtsov had been due to lead an opposition march that day, but his killing turned the event into a mourning rally.
His allies have accused the Kremlin of involvement but President Vladimir Putin condemned the murder as “vile” and “provocative”, vowing to find the killers.
Nemtsov, 55, had been walking home from a restaurant with his Ukrainian girlfriend, Anna Durytska, when he was shot four times.
Ms Durytska, a 23-year-old model, was allowed to return to Ukraine after being questioned by Russian police.
She told Russian media she had not seen the killer, who struck from behind.
Russia’s Federal Protective Service, in charge of presidential security, has said its surveillance cameras did not record the shooting because they were pointed towards the Kremlin.