Opponents said the voting for 12 regional legislatures and dozens of municipal contests were riddled with irregularities and accused United Russia of waging a dirty campaign to win votes. The party denied the allegations.

The voting offered a chance to gauge how much rising inflation, unemployment and resentment of the entrenched "party of power" have sapped its support a year before a presidential election in which Putin could return to Russia's top position.

Early results indicated that United Russia would retain its majority in the contested regions, but it faced challenges in provinces including the poor Kirov region near the Ural mountains and Tver, where the Communists were doing well.

The partial results reported by the Central Election Commission showed United Russia was ahead with 72.5 percent of votes in Chukotka, on the Bering Strait in Russia's far east.

The party was also ahead in a handful of regions further west, with 40 percent to 70 percent of the votes. No results were in late Sunday from the Russian of Kaliningrad, where a protest over economic conditions drew 10,000 people last year.

Putin, who was president from 2000 to 2008, has suggested he will either run for president in the election due in March 2012 or endorse President Dmitry Medvedev, his protege, for a second term. A parliamentary election is due in December.