Nairobi/Niamey  - Voters in Niger go to the polls on Tuesday in a controversial referendum that could allow President Mamadou Tandja to remain in power indefinitely.

Tandja, 71, has faced international criticism for dissolving the constitutional court and riding roughshod over parliament as he attempts to extend his term by another three years and remove barriers that would prevent him from running again.

There is international concern that the president's attempts to cling to power could cause instability in the impoverished nation of 15 million.

The president, who in June assumed the power to rule by decree, says that the people of the massive West African state want him to remain in charge beyond the end of 2009, when his second and final term in power expires.

According to Tandja, he needs at least an extra three years in power to oversee foreign-backed projects such as a French uranium mine and an oil refinery.

Tandja and his supporters say these projects have started to raise living standards but that they would falter if he were forced to step down.

However, Niger's opposition has accused him of attempting to become a dictator and has called on people to boycott the referendum.

The European Union, one of Niger's major donors, has suspended aid to the country and warned that Tandja's actions constitute "grave violations of core democratic values and the principles of the rule of law."

Niger's borders are expected to remain closed until midnight Tuesday while the ballot takes place. Results are expected within five days. (dpa)