(Adds ethnic groups in talks with government)

By Gopal Sharma

KATHMANDU, Feb 19 (Reuters) - A convoy of oil tankers arrived in Kathmandu on Tuesday under armed police guard, the first major delivery of fuel to Nepal's capital since a blockade led to shortages of petrol and food, officials said.

The strike and blockade, which began last week in Nepal's fertile southern plains bordering India, has been called by ethnically based protest groups to demand greater autonomy for the Terai region, home to half the country's population.

The crisis has also raised serious doubts over the government's plans to hold a national election in April.

In an attempt to ease the tension, organisers of the protests said they were in talks with authorities to explain their position and seek the government response to their demands.

The tankers began the journey from the Indian border to the capital late on Monday and, using the cover of a night curfew, arrived on Tuesday.

All Nepal's fuel and many essential goods come from India, and almost everything has to pass through the plains of the Terai to Kathmandu.

"Yes, 36 trucks carrying fuel have arrived. But that is not enough to ease the scarcity," said Purushottam Ojha, a senior official in the Ministry of Supplies.

The government has vowed to press ahead with the April 10 election for a national assembly expected to prepare a new constitution and formally declare an end to the nearly 240-year-old monarchy.

The vote is the centrepiece of a 2006 peace deal with Maoist former rebels, which allowed the insurgents to join the political mainstream. The election has already been delayed twice because of political uncertainty.

But ethnic Madheshi groups say the pact had failed to address the demands of Madheshis and have threatened to boycott the poll.

"If we are talking about fair and reasonably acceptable elections, the chances of its taking place in April are almost gone," said Yubaraj Ghimire, editor of the news magazine, Samay.

HIGHWAYS DESERTED

The strike has left the highways to the Kathmandu Valley, home to 2 million people, deserted.

Thousands of cars and motorcycles have been lining up for several hours outside the few petrol pumps in Kathmandu which remain open, while most public buses and taxis have stopped operating.

Hospitals say they are facing a shortage of oxygen, which is produced by factories in the south.

At least six people were hurt in clashes between police and protesters in the southeastern town of Biratnagar, home town of Prime Minister Girija Prasad Koirala, prompting a curfew to be imposed there.

Consumer groups said the turmoil in the south had led to the hoarding of goods such as rice, lentils and cooking gas.

"Prices of fresh vegetables and fruits have increased by 25 percent from last week," said Jyoti Baniya of the Forum for the Protection of Consumer Rights.

The people of the Terai, known as Madheshis, share closer linguistic and cultural links with north Indians than with Nepal's hill people, and want the plains turned into an autonomous region.

They have also demanded more say in central government.

At least one person was killed on Sunday and dozens were wounded when police fired on Madheshi protesters demanding electoral reforms ahead of April's election.

Similar protests last year claimed at least 45 lives. (Editing by Alistair Scrutton and Alex Richardson)

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