Authorities have extended a curfew in a town in southern Nepal, a day after at least 27 people died in a clash.
The Madheshi community wants a federal system
More than 40 others were injured in the clash between former Maoist rebels and supporters of a regional rights group in and around the town of Gaur.
Maoists and protesters seeking more rights for the Madheshi people in the south have spent months at loggerheads.
The bloodshed is the worst Nepal has seen since a truce last year which led to peace accords with the Maoists.
Nepal's Kantipur television reported that a curfew has been also imposed in the neighbouring town of Kalaiya amid reports of tension in the area.
The police say Wednesday's clashes broke out over a meeting ground in Gaur which both sides wanted to use. The sides have accused each other over the violence and of opening fire first.
A senior Maoist leader Krishna Bahadur Mahara said most of those dead were Maoist supporters. But a leader of the Madheshi, Kishor Kumar Biswas, said most of those killed or injured are local people.
Mr Mahara said the Maoists were organising processions around the country in memory of those killed in the incident.
Nepal's interior ministry has ordered an investigation into the incident.
Groups speaking for Madheshis, or southern Nepalese, have been demonstrating since December for greater rights under the country's new constitution.
The Maoists are bitterly opposed to most of these organisations, saying they themselves are the best guarantors of regional and ethnic rights.
Under peace accords, thousands of former Maoist fighters and their weapons are supposed to be confined in UN-approved cantonments.
After a peace agreement last November that effectively ended Nepal's 10-year-old insurgency, Nepalese parties are currently preparing for polls in June to elect an assembly that will write a new constitution.