Niamey - Boko Haram militants attacked an island on Niger's side of Lake Chad late on Friday and heavy fighting ensued as the army sought to repel them, residents and security sources said.
The Lake Chad area - a vast maze of tiny islands and swampland sheltering thousands of Nigerian refugees - is thought to be serving as a hideout for the Islamist insurgent group.
"There was heavy weapons and machine gun fire from about 20:00 local time," said a resident of Niger's nearby lakeside town of N'Guigmi, which Boko Haram attempted to seize earlier this month. Two security forces also confirmed the attack, without providing further details.
It was not immediately clear which island had been attacked on Friday and whether it was inhabited, but the security sources and residents said it was in Niger and within 50 km (30 miles) of the borders with Chad and Nigeria.
One of the security sources said it would provide a strategic, concealed base for the militants to co-ordinate future attacks if they won control.
Last week, Boko Haram fighters aboard motorised canoes attacked a lakeside fishing village in Chad, killing at least five people in the group's first known lethal attack on that country.
The Sunni group, which has killed thousands of people in a six-year insurgency in Nigeria, has been gaining strength in the past year. It has carved out a territory the size of Belgium in the northeast of the country and intensified cross-border raids.
But regional forces from Nigeria, Chad, Cameroon and Niger have won battles against the group in recent weeks as they seek to hem them within their heartland.
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Niger, a poor desert nation, is also seeking to dismantle clandestine Boko Haram networks around its southern border. The defence ministry on Friday raised 2 billion CFA Francs to help the army fight the jihadists via a telethon campaign.
France's foreign minister Laurent Fabius is due to arrive in Chad on Saturday as part of a 48-hour trip to countries affected by Boko Haram's insurgency. He will then travel to Cameroon and Niger.
So far the countries' former colonial master, which has a strong military presence and fighter jets in the region, says it is not directly involved in fighting Boko Haram, restricting itself to providing intelligence and logistical aid.
Military chiefs will meet in Chad's capital N'Djamena next week to finalise plans for a 8,700-strong task-force of troops from Chad, Cameroon, Nigeria, Benin and Niger to fight the militant group, although it is not clear how effective coordination will be.
The United States is also deepening its commitment to countering the group and will share communications equipment and intelligence with African allies.