Cameron condemns Nemtsov murder
David Cameron has condemned the "callous murder" of Russian opposition politician Boris Nemtsov and said the crime "must be fully, rapidly and transparently investigated, and those responsible brought to justice".
Mr Nemtsov, a leading critic of president Vladimir Putin and of the war in Ukraine, was gunned down near the Kremlin on the eve of a major rally in Moscow.
The Prime Minister said he was "shocked and sickened by the callous murder" of "a man of courage and conviction" who was "greatly admired in Britain" not least by former PM Margaret Thatcher.
"Boris Nemtsov is dead. But the values he stood for will never die," he said in a statement.
Mr Putin is reported to have taken personal charge of the investigation which his spokesman said "has all the makings of a contract hit and is extremely provocative".
Paying tribute to the murdered politician, Mr Cameron said: "His life was dedicated to speaking up tirelessly for the Russian people, to demanding their right to democracy and liberty under the rule of law, and to an end to corruption.
"He did so without fear, and never gave in to intimidation. He was greatly admired in Britain, not least by his friend Lady Thatcher, who visited him in Russia and who would have been appalled by today's news.
"The courage of Nemtsov's life contrasts with the utter cowardice of his murder.
"I extend my condolences to Boris Nemtsov's family and friends. The Russian people have been deprived of a champion of their rights."
Mr Nemtsov, said to have been hit by four shots from a passing car as he walked on a bridge, was killed hours after urging Russians to attend a protest rally and march against the "mad, aggressive and deadly policy of war against Ukraine".
The president's spokesman, offering the president's condolences, said the crime "has all the makings of a contract hit and is extremely provocative".
Critics accuse Mr Putin of creating a climate of intense intolerance of dissent.
The killing comes at a time of tense relations between Moscow and the West over Russia's support of separatist rebels in Ukraine and concerns it could move its attention to other neighbouring countries.
US president Barack Obama called on Russia's government to perform a "prompt, impartial and transparent" investigation to bring to justice the killers of the "tireless advocate".
"The Russian people, who have lost one of the most dedicated and eloquent defenders of their rights," he said in a statement issued by the White House.
Pro-democracy activist and former world chess champion Garry Kasparov said on his Facebook page: "Shot four times, once for each child he leaves behind. A man of Boris's quality no longer fit Putin's Russia.
"He always believed Russia could change from the inside and without violence; after 2012 I disagreed with this.
"When we argued, Boris would tell me I was too hasty and that in Russia you had to live a long time to see change. Now he'll never see it. Rest In peace."
Ukrainian president Petro Poroshenko said he was shocked by the killing and hoped those responsible for removing a "bridge" between the two countries would be brought to justice.
As an economic reformer, Mr Nemtsov served as deputy prime minister under the presidency of Boris Yeltsin in the 1990s, and enjoyed a successful spell as governor of a major city, but fell out of favour when Mr Putin took charge.
Council of Europe secretary general Thorbjorn Jagland said: "This political murder is a sign of the climate of hate and intolerance developing in many parts of Europe today, including in the Russian Federation. We must join forces to stop this dangerous development. I call on the Russian authorities to do their utmost to bring the killers of Boris Nemtsov to justice."
Shadow foreign secretary Douglas Alexander said: "The shocking murder of former Russian deputy prime minister Boris Nemtsov has rightly drawn widespread international criticism and condemnation.
"Mr Nemtsov was a committed democrat and made a lasting contribution to politics in Russia, including being an outspoken critic of the conflict in Ukraine.
"The priority now must be a thorough and impartial investigation into this brutal murder.
"Clearly President Putin has a responsibility to show that the Russian authorities are willing and able to take the appropriate steps to identify Mr Nemtsov's killers and bring them to justice."
Former Liberal Democrat leader Sir Menzies Campbell said Mr Putin bore some responsibility for creating the kind of atmosphere in which dissent could end in "political assassination".
"Remember, other dissidents have met their deaths in recent years as have investigative journalists, so this is not a one-off," he told Sky News.
"I am not saying that he (Putin) is responsible or that he ordered the killing or anything of that kind. There is no evidence to support that.
"But if you create an atmosphere in which those who are opposed to government find themselves subjected to what is essentially a political assassination then you have to take some responsibility."
He said the declaration that Mr Putin would take personal charge of the investigation had "induced a certain amount of scepticism both in Russia and abroad".
"It demonstrates just how difficult it is in Putin's Russia to be a dissident; to have a view which is different from the view of the Putin government.
"And for that, the fact that that atmosphere exists at all, is something for which I think Mr Putin must take responsibility."
The rally which Mr Nemtsov had been due to lead has been cancelled by organisers in favour of a demonstration to mourn his death.
Russia's top state investigation body said it was looking at several possible motives for the attack: an attempt to destabilise the state; Islamic extremism; the Ukraine conflict; and his personal life.
The politician was reported to have been with a female companion when he was shot - identified by Kremlin-friendly media outlets as a young Ukrainian model.
Amnesty International said the case must not be allowed to be added to a " list of unsolved political murders and attacks" in Russia.
Deputy director for Europe and Central Asia Denis Krivosheev said: "Boris Nemtsov was one of Russia's most prominent and courageous political activists and was a prisoner of conscience in the past when he was arrested in connection with peaceful street protest.
"He was, with others, actively planning a large opposition demonstration in Moscow on Sunday.
"In the current crackdown on freedoms of expression, assembly and association, this is a cold-blooded murder of one of those free voices whom the authorities have so actively sought to silence.
"There is already a list of unsolved political murders and attacks in Russia, the investigations of which are under the 'personal control' of senior Russian politicians. We cannot allow Boris Nemtsov to become just another name on this list.
"Until the full truth about Boris Nemtsov's killing is established, the numerous rumours that we are already seeing will persist, and they may be used by all sorts of unsavoury elements to provoke violence around the forthcoming protest events."