NIAMEY (Reuters) - Mutinous troops led by an army colonel captured Niger’s President Mamadou Tandja after a gun battle on Thursday, and said they were suspending the constitution and dissolving all political institutions.

Tensions had been high in the west African uranium exporter since Tandja changed the constitution to extend his rule last year, a move that drew widespread criticism at home and led to international sanctions.

“We, the security and defence forces, have decided to take responsibility for putting an end to the tense political situation that you are already aware of,” a spokesman for the military junta, which called itself the Supreme Council for the Restoration of Democracy (CSRD), said in a statement on state television late on Thursday evening.

The statement made no mention of Tandja, but military sources said he had been seized along with several ministers.

They said soldiers led by Colonel Adamou Harouna had stormed the presidential palace in a four-hour gun battle in the heart of the capital, Niamey.

The new military rulers’ statement said they had closed the borders and imposed an overnight curfew.

They gave no indication of how long they intended to hold power but called on Nigeriens and the international community to support their actions. The West African economic body ECOWAS said it would punish any unconstitutional power-grab.

During the day, plumes of smoke were seen rising from the palace amid heavy gunfire. Hospital sources said at least three soldiers were killed in the clashes. A Reuters witness saw five injured soldiers at a hospital.

Later a Niamey resident told Reuters: “Calm has returned and tanks have taken up positions close to the barracks, where Tandja and members of his government were rumoured to be held.”

The resident, who asked not to be named, said a soldier living next door had told her not to worry as there would be no more resistance since the entire army supported the coup.

EXPANSION OF POWER

Harouna, previously thought to be a major, heads Niger’s ECOWAS standby force. Analysts and local journalists played down the possibility of a counter-coup, saying Tandja’s presidential guard was divided and heavy weapons had been taken to barracks under the junta’s control.

Tandja drew criticism and sanctions after dissolving parliament and orchestrating a constitutional reform in 2009 that gave him added powers and extended his term beyond his second five-year mandate, which expired in December.

The reform removed most checks on his authority, abolished term limits, and gave him an initial three more years in power without an election. Tandja said he needed extra time to complete large-scale investment projects.

In Washington, State Department spokesman P.J. Crowley said the situation was “very fluid” in Niger and the United States was closely monitoring it.

“Clearly, we do not in any way, shape or form, you know, defend violence of this nature, but clearly we think this underscores that Niger needs to move ahead with the elections and the formation of a new government,” he said.

ECOWAS, which has for months tried to broker a solution to the deadlock between Tandja and the opposition, suspended Niger after Tandja extended his term. The United States terminated trade benefits, while former colonial power France also criticised Tandja last year.

Despite the political turmoil, Niger has attracted billions of dollars in investment from major international firms seeking to tap its vast mineral resources, including French nuclear plant builder Areva and Canada’s Cameco.

Areva, which has been mining uranium in Niger for decades, is spending 1.2 billion euros ($1.79 billion) on a new mine.

China National Petroleum Corp signed a $5 billion deal there in 2008 to pump oil within three years.

Tandja has faced a rebellion by northern Tuareg-led rebels. Analysts said they were unlikely to be involved in the coup.