Boris Nemtsov, a charismatic Russian opposition leader and sharp critic of President Vladimir Putin, was gunned down near the Kremlin, just a day before a planned protest against the government.

Nemtsov's death late on Friday ignited a fury among opposition figures who assailed the Kremlin for creating an atmosphere of intolerance of any dissent and called the killing an assassination.

Putin quickly offered his condolences and called the murder a provocation.

Nemtsov, a 55-year-old former deputy prime minister, was working on a report presenting evidence that he believed proved Russia's direct involvement in the separatist rebellion that has raged in eastern Ukraine since last April.

Ukraine and the West accuse Russia of backing the rebels with troops and sophisticated weapons. Moscow denies the accusations.

Opposition activist Ilya Yashin, who last spoke to Nemtsov two days before the killing, said he had no doubt that 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," Yashin said.

(Al Jazeera)