Moscow: Russia's Security Council accused the United States of plotting to oust President Vladimir Putin by financing the opposition and encouraging mass demonstrations, less than a week after a protest leader was murdered near the Kremlin.

The US is funding Russian political groups under the guise of promoting civil society, just as in the "colour revolutions" in the former Soviet Union and the Arab world, council chief Nikolai Patrushev said on Wednesday. At the same time, the US is using the sanctions imposed over the conflict in Ukraine as a "pretext" to inflict economic pain and stoke discontent, he said.

More than 50,000 people turned out in central Moscow on Sunday to mourn the death of Boris Nemtsov, a former deputy premier turned Putin opponent who was gunned down on Friday in one of the most heavily guarded areas of the capital. That was the biggest rally Russia has seen since 2011-12, when Putin was preparing to return to the presidency for a third term.

"It's clear that the White House has been counting on a sharp deterioration in Russians' standard of living, mass protests," Patrushev said. Russia can withstand the pressure, though, thanks to its resilience and "decades of experience in combating color revolutions," he said.

The Russian-backed revolt in Ukraine has led to the worst standoff between the Kremlin and the US and its European allies since the end of the Cold War. The fighting has claimed at least 6000 lives, according to the United Nations. Putin has repeatedly blamed the US for inciting the protests in Kiev last year that toppled his ally, Viktor Yanukovych.