Three Sinhalese extremists and a soldier were killed and militants torched buses on the first anniversary of an accord aimed at ending Tamil separatist violence, police said today. Most shops, offices and businesses were closed today in Colombo, the capital, and its surburbs. Police said people were afraid to open their businesses because of possible violence by Sinhalese radicals opposed to the Indian-brokered peace accord. A 24-hour curfew went into effect at 6 a.m. today in the island's south after radical Sinhalese nationalists called for a general strike. Residents in the northern city of Vavuniya, about 125 miles northeast of Colombo, said by telephone that Indian soldiers also declared curfews in some areas in the island's north and east until Sunday morning to prevent attacks by Tamil rebels. The peace accord is opposed both by Tamil rebels fighting for five years for independence in the north and east of the island and by the Peoples Liberation Front, an extremist group from the island's majority Sinhalese community. The Sinhalese say it makes too many concessions to the minority, while the Tamils say it does not meet their demands for independence. Three men were killed by police in separate incidents in which Sinhalese extremists tried to attack government property, a police spokesman said on condition of anonymity. He said a Sinhalese Sri Lankan soldier was fatally shot in a battle with extremists in Hambantota district in the south. In southern and central Sri Lanka, strongholds of the Sinhalese extremists, at least eight government-owned buses were set afire Thursday night and this morning, the police spokesman said. Electricity supplies to at least four towns in southern Sri Lanka were cut Thursday night after Sinhalese extremists bew up electrical transformers, he said. A railroad engineer was injured when his train was hit by a firebomb as it pulled into Colombo, police said. Only a few government-owned or private buses were seen running. In the island's north, nearly 50,000 Indian soldiers deployed under the peace accord were put on alert after Tamil rebels called for a demonstration to protest the peace pact. On Thursday, 14 Sinhalese farmers were killed by Tamil rebels near Padaviya village, about 100 miles northeast of Colombo. The peace accord, signed by India and Sri Lanka on July 29, 1987, calls for the government to grant limited autonomy to minority Tamils in exchange for the rebels giving up their fight for a separate Tamil nation. India agreed help disarm the Tamil rebels. But violence has persisted in the Tamil areas of the north and east because the main Tamil rebel group, the Liberation Tigers of Tamil Eelam, refused to accept the accord. India is involved in the conflict because of the sympathy of its own Tamil minority of 60 million for the island conflict. Before the peace pact was signed, Sri Lanka regularly accused India of training and supplying the rebels. More than 8,000 people have been killed since the ethnic war began in 1983. Tamils, who are mostly Hindus, make up 18 percent of Sri Lanka's 16 million people and say they are discriminated against by the Sinhalese. The Buddhist Sinhalese make up about 75 percent and control the government and the army. More than 400 people have been killed since the accord was signed in attacks blamed on Sinhalese extremists. Most of the victims have been government officials or members of the governing United National Party of President Junius R. Jayewardene, who signed the accord.