Officials in southern Nepal say a bomb blast has killed four people and wounded at least 20 others.

Authorities say a bomb attached to a motorbike exploded Monday in Janakpur during a demonstration by protesters demanding a separate province for Maithili-speaking people.

The Nepalese parliament is nearing a deadline to write a new constitution which will divide the country into new states. Various groups across the country have been demanding provinces based on ethnicity.

Nepal has been relatively peaceful since Maoist rebels signed a peace deal in 2006, ending their decades-long insurgency.