UPDATE 1-Niger leader dissolves constitutional court

* Tandja dissolves constitutional court

* Appoints eight new pro-referendum ministers

* Radio station taken off air

(Releads with dissolution of court, adds army reaction)

By Abdoulaye Massalatchi

NIAMEY, June 29 (Reuters) - Niger's president dissolved the constitutional court on Monday, hours after he appointed eight new ministers from parties that back his plan for a referendum on extending his stay in office.

The court said this month that President Mamadou Tandja's scheme was unlawful, but the president of the uranium-exporting West African country has vowed to press ahead anyway.

Tandja was due to step down when his term ends later this year, but he wants a referendum on Aug. 4 on whether he should be able to lead Niger for at least three more years.

The referendum plan has raised concerns among regional political bodies and Western donors, who fear it is a sign of back-sliding on democracy. It has also brought protests by unions and the opposition at home.

Niger's armed forces said on Monday they would remain independent, after the anti-referendum coalition called upon them at the weekend to disobey orders.

"The Nigerien armed forces will not serve partisan interests," defence ministry spokesman Colonel Goukoye Abdoulkarim said on state radio. "They ask the different actors to exclude them from politics once and for all."

Tension rose when Tandja announced on Friday he would rule by decree after Niger's highest court again told him the referendum would be illegal.

The eight ministers who joined the 33-member cabinet on Monday replace those from Tandja's former ally, the Democratic and Social Convention party, which walked out of his government last week in protest over the referendum.

The new ministers all belong to parties that back the vote.

In a sign of a tougher government stand, a private radio station was taken off air on Monday after broadcasting an opposition statement. Tandja's foes demand that he step down and have called on security forces to disobey his orders.

The landlocked former French colony of 15 million people is one of the world's poorest countries.

Tandja says he needs the time to introduce a fully presidential system of government that will give the president more power and end current blockages in governance.

He also says people want him to complete large infrastructure projects, including a hydro-electric dam, an oil refinery and a uranium mine that will make Niger the world's second biggest producer of the nuclear fuel. (Editing by Daniel Magnowski and Richard Meares)