Bomb explosions in two key cities in Nepal wounded at least 13 people on Monday while Nepali politicians held last-minute rallies on the last day of campaigning before this week's poll.

One bomb, hidden behind fruit and vegetable carts, exploded at a busy market in Birgunj city in southern Nepal, wounding 12 people, police said. The city is a key transportation hub near the Indian border 100 miles south of the capital, Katmandu.

Police Chief Yogeswor Romkhani said by telephone there were no suspects and no one had claimed responsibility.

Earlier, an attacker on a motorcycle threw a bomb near the site of an election rally in Katmandu, hurting at least one person but not causing any major damage, said Home Ministry spokesman Ekmani Nepal.

The attack came minutes after a rally was held in the area by the Rastriya Prajatantra Party, a small group that is contesting Thursday's election for a Constituent Assembly that will decide the Himalayan nation's political future.

Police official Mahendra Bhattachand said police were searching for the attacker and no one had claimed responsibility for the attack. It was the third bombing in the capital in four days.

Some 17.6 million people are eligible to vote in Thursday's election to choose the assembly, which will rewrite the constitution and decide key issues for Nepal's future political system.

The election is also the first since communist rebels quit their armed struggled against Nepal's government and joined the political mainstream

Security has been stepped up, with thousands of police officers fanning out across the country, the Home Ministry said. The government has hired helicopters to patrol mountainous areas and fly police to trouble spots.

Former U.S. President Jimmy Carter and other international election monitors were to arrive in Katmandu later Monday to observe the voting.