Four men died and seven were injured on Sunday in three separate explosions in Kathmandu, Nepali police said.
There was no immediate claim of responsibility but police said they suspect the involvement of a Maoist splinter group whose pamphlets were found in a house where one of the explosions took place.
A powerful blast inside a shop killed three people and injured four, while the explosion at a home about four kilometres away left one dead and another injured.
Two more were injured when an explosive they were carrying on a motorcycle on the outskirts of Kathmandu exploded.
Security personnel also defused explosives in other areas.
“We are investigating all incidents and have stepped up the security,” police spokesman Bishwa Raj Pokharel told AFP.
Pokharel said that seven people have been arrested so far.
The incidents come on the eve of a nationwide strike called by the same Maoist splinter group, protesting death of their cadre in a police encounter over a week ago.
Nepal has enjoyed a relatively peaceful environment since the end of a decade-long civil war which concluded with a peace deal struck in 2006.
But some former guerrillas have broken away, accusing its leaders of betraying their original revolutionary ideals.
In February, the group was implicated in an explosion that killed one person outside the office of a telecom company, Ncell, part of Malaysia-based Axiata Group Berhad.
The government outlawed the group following the incident, banning their activities.