Niger's president has dissolved parliament after the country's constitutional court ruled against plans to hold a referendum on whether to allow him a third term in office.

Mamadou Tandja gave the order to dissolve the legislature on Tuesday, hours after the court said a move by the ruling coalition to hold a public vote on a third presidential term was illegal.

"On the advice of the prime minister and the speaker of parliament, the president of the republic signed today ... a decree dissolving parliament," state radio said.

Tandja's attempt to change the constitution has prompted demonstrations across the country and has been opposed by several members of his coalition government.

His second term in office is set to expire later this year but the government sought a vote on constitutional changes to allow him to run in elections scheduled for November.

According to the constitution, a new parliament will now have to be elected within three months, but there was no immediate presidential announcement on a new election date.

Referendum opposed

About 20,000 people protested in Niger earlier this month against the referendum plan, while about 20 political parties and civil groups have set up an anti-referendum coalition, the Front for the Defence of Democracy (FDD).

The Economic Community of West African States (Ecowas) has said that countries in the region could impose economic sanctions on Niger if its democracy is undermined.

Richard Moncrieff, a West Africa analyst at the International Crisis Group (ICG), said that Niger was at risk of becoming unstable amid the battle by Tandja to extend his rule.

"In the context of rising uranium revenues the attempt by the president to extend his mandate has split the political class, including his own governing coalition," he said.

"The history of the country shows that the military tend to step in to arbitrate crises like this, and the current international ambiguity surrounding military coups in Africa is indicative of the dangers this poses."

Uranium resources

Alioune Tine, the president of the African Assembly for the Defence of Human Rights, a regional rights body, said the move to dissolve the parliament looked like "a political coup d'etat".

"This political mistake is deeply regrettable ... Niger cannot take a step back after all the efforts," he said.

Resource companies have targeted Niger for investment in mining its uranium deposits in recent years.

Areva, a French state-owned company, runs two mines in Niger and is developing Imouraren, another project in the north of the country.

China and South Korea also have lucrative uranium mining deals with Niger.

The East African nation is still battling to end a two-year rebellion by Tuareg fighters.