By Gopal Sharma

KATHMANDU (Reuters) - Opponents of Nepal's Maoist prime minister hurled stones at rivals and erected barricades in a provincial town on Wednesday, police and media said, raising tensions that threaten a peace process in a country still recovering from a decade of civil war.

At least two dozen people were injured in Dailekh, 300 km (185 miles) west of the capital, Kathmandu, where activists from seven opposition parties, calling for Prime Minister Baburam Bhattarai to resign, massed outside the venue of a Maoist conference. Police fired tear gas to try to disperse the crowds.

A building housing the local Maoist party office was set on fire, police said. Opposition activists blocked the main roads leading into town and burned tires to enforce a general strike against the government, witnesses said.

"The trouble started after the main Maoist conference had ended when rival groups pelted stones at each other forcing police to fire several shells of teargas to bring the situation under control," said police spokesman Keshav Adhikari.

Television news channels said more than 25 people were injured but Adhikari said he had no figures. TV footage showed black smoke rising from burning tires and activists chanting and pumping their fists into the air.

This is the first time the Maoists and opposition parties have clashed since parliament was dissolved in May, having failed to finalize a new constitution seen as key to the country's long term stability.

The opposition parties want Bhattarai to quit to pave the way for the formation of a national unity government to oversee parliamentary elections expected in May, a demand the former rebel leader has refused.

Pressure on Bhattarai, 58, is mounting after he failed to hold the elections he ordered for November last year.

The Maoists waged an armed struggle against the country's now toppled monarchy. They joined the political mainstream in 2006 after the end of the civil war that killed more than 16,000 people. They won elections two years later and are now leading a coalition government in the impoverished Himalayan republic.

(Reporting by Gopal Sharma; editing by Matthias Williams and Ron Popeski)