Updated

Tens of thousands have gathered in downtown Moscow in the largest anti-government demonstration since 2012, protesting against Sunday's Kremlin-backed referendum in Crimea on whether to break away from Ukraine and merge with Russia.

Demonstrators waved Russian and Ukrainian flags on Saturday while opposition activists — including the two members of the punk band Pussy Riot who served prison terms for an anti-government stunt — shouted "Say no to war!" and "Putin, go away!" from a stage.

Not far away near the Kremlin, several thousand people dressed in matching red costumes marched in formation to show their support for Russian intervention in the region.

Support for reclaiming Crimea, where a majority of residents speak Russian, has intensified amid relentless state television coverage of the region.