Officials say 21 people have been killed and hundreds hurt in clashes over the past month between protesters and police in the Terai region, situated in Nepal's southern plains and home to most of the Madhesis.
The protesters want an autonomous region for the southern plains within a federal state.
They say Nepal's ruling powers are dominated by people from the mountain areas who have denied Madhesis fair representation in parliament, as well as a fair share of jobs in the government, police and army.
The protests from the Madhesi People's Rights Forum have overshadowed a peace deal between the government and Maoists aimed at ending a decade-old conflict between the two groups, which has killed more than 13,000 people.
The government says it is ready for talks, but protest leaders insist Krishna Prasad Sitaula, the home minister who Madhesi leaders accuse of using "excessive force", must resign before negotiations take place.
Girija Prasad Koirala, the Nepali prime minister, was meeting leaders of the ruling government alliance and Maoists to discuss the unrest on Wednesday.
The trouble started in January from the town of Lahan in the same region where a Maoist activist shot dead a protester.