(Recasts throughout with funerals, quotes, U.S. statement) By Gopal Sharma KATHMANDU, March 23 (Reuters) - Thousands joined weeping relatives on Friday during a mass funeral in Nepal for victims of this week's clashes between Maoists and ethnic Madhesis, the worst violence in the country for months. At least 27 people, nearly all of them Maoists, were killed in Wednesday's violence in southern Nepal, the deadliest unrest involving Madhesis and former Maoist guerrillas since the Madhesi People's Rights Forum started protests in January. The forum is demanding more government jobs and parliament seats for their ethnic community, which dominates Nepal's southern plains that border India. At the mass funeral in Kathmandu, sentiments were raw. "Oh my dear, where have you gone, leaving us behind" said a weeping Rup Sagar Upadhya, her head pressed to the chest of her husband's body, one of the victims of the violence and a Maoist. The body was kept in an open wooden coffin. Her 10-year-old son, Chandan, touched the feet of the corpse with his forehead. Minutes later, the child lit a funeral pyre in a traditional Hindu cremation. Similar rites were performed for most of the other victims who were cremated on the banks of the holy Bagmati river, close to a centuries-old Hindu shrine. The killings have sparked anger among the Maoists, who ended their revolt against the country's monarchy in November as part of a peace deal with the government. "DECLARATION OF WAR" "The reactionaries have declared a war on us," Maoist leader Baburam Bhattarai told a condolence meeting before the funeral, where 25 bodies shrouded in white cloths were displayed in wooden coffins. Two bodies were kept in the southern town of Hetauda. "If the government wants to stop us from retaliation, it should arrest the killers, declare the deceased martyrs and pay compensation to their families," Bhattarai told mourners. On Friday, the government gave a panel headed by a judge 15 days to submit its report on Wednesday's killings in the border town of Gaur, 80 km (50 miles) southeast of Kathmandu. But the Maoists have rejected the panel and demanded immediate action against the Madhesi forum. Maoist deputies disrupted the interim parliament to protest the killings. On Wednesday, Maoists and supporters of the Madhesi forum attacked each other with guns, knives and stones following a row over the selection of the same venue for public meetings. The United Nations said the killings exposed the lack of effective policing in many parts of the country, a problem which needed to be addressed as a priority. The Maoists, Madhesi forum and all political groups must "clearly and definitively renounce violence in advancing their political cause", the U.N. said in a statement in Kathmandu. The United States said Nepal's peace process could be imperiled by further violence and called for effective dialogue with ethnic groups to consider the grievances. The Maoists, who began fighting against the monarchy in 1996, signed the peace deal to end their revolt that killed more than 13,000 people. The forum says Madhesis have been discriminated by Nepal's political elite, resulting in under-representation in government jobs, parliament and the police. At least 58 people have died this year in Madhesi protests that have overshadowed the government's peace deal with the Maoists, which envisages the former rebels joining an interim administration before constituent assembly elections this year.