Russia launched an investigation on Thursday into the country's chief independent election watchdog, in what the group described as the culmination of a state-sponsored campaign to silence the monitor just three days before parliamentary polls.

Moscow city prosecutors said in a statement the investigation followed a complaint filed by lawmakers objecting to watchdog Golos's foreign financing and calling for it to end vote monitoring.

The complaint echoed Vladimir Putin's speech on Sunday at his United Russia party congress, where he accused foreigners of funding his political opponents in what reminded some of the anti-Western rhetoric that marked his 2000-08 presidency.

Putin, now prime minister, is expected to easily recapture the presidency in March, but opinion polls show Sunday's vote could weaken his party's dominance in the lower house.

Golos employees told Reuters prosecutors had served the group with a "speedy" court order to hear its case on Friday.

"This a premeditated campaign, which started with attacks in the press, but is now making use of law enforcement agencies," said Grigory Melkonyants, the deputy head of Golos.