In a stinging rebuke to the authorities and United Russia, election observers said Monday that weekend municipal elections in a provincial town had been too tarnished by fraud to be considered legitimate. The Ryazan region town of Kasimov had turned into a key battleground for the political opposition ahead of Sunday’s vote for the municipal legislature, and activists had hoped to ensure a fair election in this corner of the country following disputed national elections in December and March. According to preliminary results, United Russia won nearly 50 percent of Sunday’s vote, matching its local result in State Duma elections in December, and secured 13 seats in the 20-seat legislature. But monitors said they witnessed numerous offenses, including ballot stuffing, at the town’s 22 polling stations. “There were nearly two serious violations at every station. … The number of violations per voter was unprecedented,” said Sofia Ivanova, regional coordinator of the election watchdog Golos. Pro-United Russia ballot stuffers were caught in the act in at least two polling stations, and observers discovered stacks of votes for the ruling party at several others, she said by telephone.