Suspected Boko Haram militants attacked a Niger army base on an island in Lake Chad, leaving many soldiers dead.
Niger military sources said hundreds of armed militants riding on motorized canoes attacked the island of Karamga early Saturday, their second attempt to capture it since February, army and government sources told Reuters.
A second army source told Reuters a counter-attack to clear the island of militants was ongoing Sunday.
The number of casualties was not release, but unnamed officials say the military might have suffered "heavy losses."
The defense ministry said in a statement that operations are ongoing, with the aid of allies, aimed at clearing the island of militants.
Niger along with Chad, Cameroon, and Nigeria all border Lake Chad and are part of a multinational force fighting Boko Haram in and along the borders of northeastern Nigeria.
Boko Haram has carried out a campaign of terrorism since 2009 to turn Nigeria into an Islamic state, and has recently spread across the borders to attack towns in neighboring Cameroon, Chad and Niger. The militants have killed thousands of people in their six-year insurgency.
The United Nations Children Fund said that 800,000 children have been displaced by Boko Haram violence, nearly half the 1.5 million people uprooted by the militants' campaign.
Lake Chad's islands, which lie in dense swampland, are an ideal base for mounting surprise attacks on the countries bordering the lake: Chad, Cameroon, Niger and Nigeria, Reuters reported.
Some material for this report came from Reuters.