Jan. 31 (Bloomberg) -- The United Nations called on Nepal's political parties to ensure the April 10 parliamentary election is free of violence after a bomb attack on a rally in the country's south.

``Political differences must be resolved through peaceful means,'' UN envoy Ian Martin said in a statement yesterday, following the attack in the town of Birgunj on the border with India. ``Acts of terror will discredit whatever cause they are claimed to promote with the Nepalese people as well as the international community.''

More than 20 people, including a district officer, were injured when two bombs exploded outside a stadium in the town yesterday as the seven parties in the coalition government held a rally, Nepalnews.com reported. Armed groups in the southern Terai region bordering India telephoned local radio stations claiming responsibility for the attack, according to the report.

Nepal is holding its first national ballot since a peace accord with the rebel Communist Party of Nepal (Maoist) in November 2006 ended a 10-year civil war. Ethnic minority groups in Terai are demanding greater rights and at least 25 people were killed last year when general strikes and demonstrations in the region turned violent.

Two organizations from Terai claimed responsibility for bomb attacks in the capital, Kathmandu, in September last year that killed two people and injured more than 20 others.

Terai Army

The Terai Army, which is pressing for greater rights for the south, claimed responsibility for a bus fire earlier this month that killed seven people and injured more than 20 others in the region's Bara district, Nepalnews.com said at the time.

Eight people were injured in a bomb attack at an election rally in Kathmandu earlier this month, Nepalnews.com reported, without saying whether any groups claimed responsibility.

The Terai region lies on one of the main trading routes to India. Nepal sends almost 68 percent of its exports to India and its southern neighbor accounts for about 62 percent of Nepal's imports, according to U.S. government data for 2006.

Security in the region has ``diminished markedly'' and there are now more than two dozen armed and criminal groups operating there, UN Secretary-General Ban Ki-moon said in an October report.

Members of the Madhesi, an ethnic group in Terai, say they are discriminated against by Nepalis from the hills and underrepresented in government and state institutions.

New Constitution

The government has pledged that a new constitution to be drawn up after the ballot will give greater rights to the more than 40 ethnic minority groups in the Himalayan country of about 29 million people.

Prime Minister Girija Prasad Koirala said two days ago he will meet Madhesi demands for greater political rights as long as they participate in the April elections.

The UN last week called on the government to hold ``urgent'' talks with ethnic groups to ensure they take part in the vote. It also asked India to control suspected supporters of groups causing unrest in the Terai region.

``We ourselves should solve the problems in different parts of the country,'' the Press Trust of India cited Nepal's Home Minister Krishna Prasad Sitaula as saying yesterday. He praised India's ``decisive help and cooperation'' in the peace process.

To contact the reporter on this story: Ed Johnson in Sydney at ejohnson28@bloomberg.net.

Last Updated: January 30, 2008 20:00 EST