Fuel supplies to the Nepalese capital, Kathmandu, have almost completely run out because of a road blockade in the south of the country, officials say.
Correspondents say that if the blockade continues, elections scheduled for 10 April could be in jeopardy.
The blockade is part of a general strike staged by an ethnic group of the southern plains - or Terai - who want more rights and representation.
Roughly 90% of Nepal's imports travel from India via the southern roads.
Queues
Officials say that clashes broke out in the town of Nepalgunj - on the border with India - over the weekend and at least one person was killed and about 60 police and protesters injured.
"Madheshis should recognise that the constituent assembly election offers them unprecedented access to political power"
Nepalese petrol stations have been severely hit by fuel shortages, largely triggered by protesters blockading key roads in the south of the country.
Most petrol stations have shut down and those still serving fuel have attracted queues of thousands of motorists.
The Madheshi community in the Terai say that they have been excluded from a peace deal in 2006 between the government and Maoists.
"The state has neglected us, not respected our demands and instead accused us of trying to break the country," a spokesman for the United Democratic Madheshi Front (UDMF) told reporters in Kathmandu.
"The state can try and crush us and our movement, but our struggle will continue."
Dozens of people died when Madheshi protests turned violent last year, casting a pall over the fledgling peace process.
The Terai area comprises about half of the country's population, and is known as the country's bread basket.
Nearly all of Nepal's fuel supplies from India come across the southern border but the violence has meant that transport drivers are refusing to deliver fuel and other essential supplies.
Correspondents say that the problem has been exacerbated because Nepal has been slow in paying for some of the fuel received from India.
Former US president Jimmy Carter, whose Carter Center employees are monitoring the April election, urged the government and Madheshis to settle their disputes amicably.
"Madheshis should recognise that the constituent assembly election offers them unprecedented access to political power," Mr Carter said in a statement.
"I encourage all sides to seek compromise in the best interest of Nepal."
The UN has also warned that continued unrest will threaten polls in which voters will select a body to rewrite the constitution that will probably culminate in the abolition of the country's 239-year-old monarchy.
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