Kathmandu: Four people were killed and more than 20 wounded when a bomb attached to a motorbike went off near a crowd of protesters in southern Nepal on Monday, police said.
The group of 150 demonstrators had been staging a sit-in protest when the bike exploded in the religious hub of Janakpur, 20 kilometres from the Indian border, said local police Chief Basanta Raj Gautam.
"One of the protesters died on the spot while three died on their way to hospital. We have referred around seven seriously injured victims for treatment to Kathmandu," he told Agence France Presse (AFP).
"Over 20 people who sustained minor injures from the blast are being treated at various hospitals in the district."
Nepal has enjoyed an uneasy calm since rebel Maoists waged a 10-year war against the government until a peace accord was signed in 2006.
The country's Parliament is nearing a deadline to write a peacetime constitution which will divide the the country into federal provinces, and the protesters had been pressing their demands with a city-wide strike.
"There were around 150 persons sitting in the protest... when the bomb went off. We have increased security in the area but no one has taken responsibility for the incident," Mr Gautam said.
"The strike was called by the Mithila State Struggle Committee for three hours on Monday and their cadres had blocked road transportation to pressure for a separate Mithila province in the constitution."
Uma Shankar Singh, a sub-inspector of police, said that the bomb had been fitted on the tail box of the motorcycle. No one has been arrested in connection with the attack.
Bomb attacks have been relatively rare since the end of the insurgency, although a powerful blast in Kathmandu in February killed three people and wounded seven in the first such incident in the capital for three years.
An organisation calling itself the United Ethnic Liberation Front (UELF) has claimed responsibility for the blast although their motives still remain unclear.