Police in Serbia have fired tear gas to prevent hundreds of opposition supporters from entering the capital’s city council building. A crowd was outside Belgrade city hall on Sunday to protest what election observers said were widespread vote irregularities during a general election a week ago. The country’s populist authorities have denied rigging the vote. President Aleksandar Vucic said Sunday that those claims were blatant ”lies” promoted by the political opposition. Shielded riot police barricaded themselves inside Belgrade’s city hall, firing tear gas as hundreds of opposition protesters broke windows on the entrance of the downtown building. There were no immediate reports of injuries.