A top rebel commander in Nepal has vowed to keep up attacks on government forces after one of the worst battles between the two sides in recent months. Government forces say they killed about 500 rebels in the west of the country during fierce fighting over the past days.

The rebel commander Prachanda says his forces remain undeterred by heavy fighting with government troops Saturday and he has vowed to continue the military campaign against them.

The statement came late Sunday after fierce fighting between the Maoist guerrillas and government forces in the mountain town of Beni, some 280 kilometers west of the capital Kathmandu.

Officials say fighting raged for 12 hours and government forces killed as many as 500 rebels. But that figure has not been independently confirmed. Rebels say they lost about 40 fighters.

Human rights groups say the battle was the second major clash between Maoists and the government in recent weeks. One rights worker says the surge in fighting may be a reaction to recent statements made by the government.

Charan Pasarai is with the Human Rights Organization of Nepal, or HURON. "Before that the government was saying that they are winning the war with the Maoists and the Maoists have weakened, [the Maoist movement]," he says. "It has retaliated to that kind of statement by the government."

The Maoists, who are also called the Communist Party of Nepal say they are inspired by China's revolutionary leader Mao Zedong. They have been fighting the Nepalese government since 1996 in an attempt to overthrow its monarchy. Fighting has intensified since August, when the rebels pulled out of peace talks, causing the collapse of a seven-month ceasefire.

In recent weeks, Maoist leaders have called for international mediators to oversee a new round of peace negotiations with the government. At the same time, however, the United Nations and other aid agencies have threatened to pull out of Nepal because the rebels are constantly trying to extort money from aid workers.

Despite that contradiction, Mr. Pasarai says it is important to give the rebels a chance to return to the negotiating table. "I think at this point we cannot really judge whether they are sincere," he says. "But if we accept their proposal and see whether they would abide by what they would have said, whether they would put those words into action, I think that's important to see."

So far the government has refused to accept the rebels proposal for international mediation in peace talks.

Both the government and the rebels claim to control the area near Beni, where the fighting took place. More than 9,000 people have died in the eight year insurgency.