Russian police on Tuesday raided the offices of election watchdog Golos as well as the homes of its employees, a lawyer for the group said, amid an ever-increasing crackdown on independent voices in the country.

Earlier Tuesday police raided the homes of several Golos employees, including the apartment of senior executive Grigory Melkonyants and confiscated equipment including computers.

"They are searching the offices as we speak," a Golos lawyer, Olga Gnezdilova, told AFP.

Police have linked the raids to a tax investigation against the head of the group's branch in the Volga city of Samara, but Golos described the searches as the latest salvo in a campaign to intimidate it and other Kremlin critics.

Over the past few years the independent monitor group Golos (Voice), which has documented widespread claims of election fraud, has been targeted by a campaign of intimidation including accusations of serving US interests.

Melkonyants said that with the raids authorities have taken their attempts to "strangle" Golos to a new level.

"They've now resorted to extreme measures," he said in remarks broadcast on independent television channel Dozhd.

He chalked up the raids to the group's plans to monitor local elections across Russia this autumn.

"An election campaign has started for Golos in earnest," he said on Twitter.

Critics accuse authorities of seeking to snuff out the last signs of dissent on the back of patriotic euphoria and anti-Western sentiment triggered by Moscow's seizure of Crimea and several rounds of Western sanctions over the Ukraine crisis.

Registered as a "foreign agent," Golos will not receive any state funding next year and has been forced to launch a public appeal to prevent a cash shortfall.

Russia's opposition led by top activist Alexei Navalny has vowed to run in parliamentary polls next year as well as local elections this autumn, though they could be barred by authorities from entering the race.

Authorities are seeking to bring forward by three months parliamentary elections that were intially scheduled to take place in December 2016.