Several people hurt in explosions targeting election rally of a mainstream party.
Prachanda has accused security forces of plotting to undermine the elections in order to save King Gyanendra from losing his throne.
The assembly’s first tasks will to abolish the monarchy and rewrite the constitution.
King Gyanendra, viewed by supporters as the incarnation of the Hindu god Vishnu, the protector, also made a rare public statement.
“We call upon all adult citizens to exercise their democratic right in a free and fair environment,” he said.
In the latest death of the campaign, one protester died when police have opened fire on demonstrators angry at the slaying of an election candidate the previous day.
Ram Kumar Khanal, an area police chief, said the police had opened fire with live ammunition in order to disperse protesters who were smashing stores and buses.
Nearly one-third of its people live on an income of less than a dollar a day
Eighty per cent of Nepalis are Hindus
Nepal was the world’s last Hindu kingdom before declaring itself officially secular in 2006
A new polling date will be chosen in about a week for the constituency in Jahare Bazar town, Binod Kumar Pokhrel, an election official was reported by the Associated Press as saying.
On Tuesday, six former Maoist rebels were shot dead by police during clashes with supporters of the rival Nepali Congress party in Dang district, 300km west of Kathmandu.
Campaigning has also been marred by reports of intimidation by Maoist loyalists, many of whom have failed to adapt to civil life after years spent fighting government forces.
Bhoj Raj Pokhrel, the chief election commissioner, said: “we are all concerned regarding election day violence”.
The European Union, which has sent a 120-strong election observation team, repeated calls for a violence-free election.
“I call again on all those involved in the election to respect the fundamental right of every Nepali citizen to cast their vote on April 10 in a peaceful atmosphere without fear of intimidation or violence,” Jan Mulder, the chief observer, said.
The 27 million people of the Himalayan nation between India and China will be hoping that the election can bring peace and prosperity.
“We have no choice but to be hopeful,” Biraj Shresthra, a 43-year-old who runs a Kathmandu electronics shop, said. “We’ve seen so much fighting. Maybe now it will stop.”