BUJUMBURA (Reuters) - Burundi's army spokesman said 33 people were killed on Tuesday in an attack by Hutu rebels south of the capital Bujumbura, state radio said on Wednesday. Lieutenant Colonel Isaie Nibizi said rebels attacked the town of Rumonge, 75 km (45 miles) from Bujumbura at 7.30 p.m. (1730 GMT) and a battle raged until Wednesday morning. Nibizi told state radio that 20 rebels, 12 civilians and a government soldier were killed and four soldiers and eight civilians wounded in the attack. He gave no other details. The attack brings to over 100 the number of people killed in the past four days in fighting in the tiny African country. The army said on Tuesday that 76 people had died last week in fighting northeast of the capital Bujumbura. At least 274 died near the capital's airport on January 1 in what the army described as the biggest attack ever by Hutu rebels. The main Hutu rebel group vowed on Tuesday to press on with its guerrilla war against Burundi military leader Major Pierre Buyoya to force a negotiated settlement to the country's ethnic conflict. But the rebel National Council for the Defence of Democracy (CNDD) denied at a Nairobi news conference that its armed wing, Forces for the Defence of Democracy (FDD), had targeted civilians. The denial followed almost daily reports from Burundi's Tutsi-led army of killings of civilians blamed on Hutu rebels. Government officials and many Tutsi citizens say the CNDD is bent on a genocide against Tutsis, similar to the 1994 Rwanda genocide in which an estimated 800,000 Tutsis and some moderate Hutus were killed by hardline Hutu militia and soldiers. Hutu rebels in Burundi and Rwanda have stepped up attacks against military, civilian and economic targets since the start of December in a campaign that analysts say appears coordinated. At least 150,000 Burundians, mostly civilians, have died since unrest erupted in October 1993 when the country's first elected Hutu president, Melchior Ndadaye, was killed by Tutsi troops in a coup bid. Buyoya, a retired Tutsi major and former military ruler, took power in a coup in July 1996, ousting a Hutu government. Regional states imposed sanctions on Burundi after the coup.