Ex-deputy PM shot dead in Moscow
Charismatic former deputy prime minister-turned Russian opposition leader Boris Nemtsov has been killed in a drive-by shooting on a Moscow bridge.
His death comes just a day before a planned protest against President Vladimir Putin's rule. The Kremlin said Mr Putin would personally oversee the investigation.
Mr Nemtsov, 55, was a sharp critic of Mr Putin, assailing the government's inefficiency, rampant corruption and the Kremlin's policy on Ukraine, which has strained Russia-West ties to a degree unseen since Cold War times.
The Interior Ministry, which oversees Russia's police force, said Mr Nemtsov was shot four times from a passing car as he was walking on a bridge just outside the Kremlin shortly after midnight.
Mr Nemtsov served as deputy prime minister in the 1990s and once was seen as a possible successor to Boris Yeltsin, Russia's first elected president.
After Mr Putin was first elected in 2000, Mr Nemtsov became one of the most vocal critics of his rule, helping to organise street protests and writing extensively about official corruption.
Interior Ministry spokeswoman Yelena Alexeyeva said Mr Nemtsov was walking with a female acquaintance, a Ukrainian citizen, when a vehicle drove up and unidentified assailants opened fire. The woman was unhurt.
Opposition activist Ilya Yashin told Ekho Moskvy radio that he last spoke with Mr Nemtsov two days before the killing. Mr Nemtsov was working on a report presenting evidence that he believed proved Russia's direct involvement in the separatist rebellion that erupted in eastern Ukraine last year.
Ukraine and the West have accused Russia of backing the rebels there with troops and weapons. Moscow has denied the accusations, but large numbers of sophisticated heavy weapons in the rebels' possession has strained the credibility of its denials.
Mr Yashin said he had no doubt that Mr Nemtsov's murder was politically motivated.
"Boris Nemtsov was a stark opposition leader who criticised the most important state officials in our country, including President Vladimir Putin. As we have seen, such criticism in Russia is dangerous for one's life," he said.
Political analyst Stanislav Belkovsky told the radio station that he did not believe that Mr Nemtsov's death would in any way serve Mr Putin's interests.
"But the atmosphere of hatred towards alternative thinkers that has formed over the past year, since the annexation of Crimea, may have played its role," he said, referring to the surge of intense and officially-endorsed nationalist discourse increasingly prevalent in Russia since it annexed Ukraine's Crimean Peninsula.
Mr Nemtsov was one of the organisers of the Spring March opposition protest set for Sunday, which comes amid a severe economic downturn in Russia caused by low oil prices and Western sanctions.