Fresh protests have broken out in parts of southern Nepal over the country’s new constitution, adopted on Sunday. Demonstrators have blocked two of the main border crossings from India, shutting off vital supply lines.

The protesters, who belong to ethnic groups from the southern lowlands, say the new constitution marginalizes them. In Kathmandu, Prime Minister Sushil Koirala has been meeting the leaders of Nepal’s three main political parties to try to find a solution to the crisis.

At one southern town, Birgunj, hundreds of riot police have used tear gas to try to break up demonstrations. Reporters in Birgunj say the protesters are effectively shutting off the country’s main supply line. With several hundred trucks stuck at the frontier, supplies including sugar, salt and cooking gas cylinders are being affected. Nepal is heavily dependent on supplies from neighboring India. According to reporters in Kathmandu long queues are forming at petrol stations as residents stockpile fuel in anticipation of shortages.

Nepal’s new constitution defines the majority Hindu nation as a secular republic divided into seven federal provinces. But ethnic groups in southern Nepal want more territory and rights for ethnic federal states.