Niamey (AFP) - Boko Haram militants attacked troops from Niger on an island base in Lake Chad, the government said on Saturday, in a raid believed to have taken a heavy toll on the army.

"At dawn on April 25, fighters from the terrorist group Boko Haram riding motorised canoes attacked the island of Karamga, a position northwest of of the town of Bosso held by our defence and security forces," the ministry of defence said.

"Operations are ongoing with the support of partners to counter the ambitions of this terrorist group," the ministry added in a statement broadcast on television.

The ministry did not indicate if there were any casualties as a result of the raid.

An official from Diffa, the capital of the southeast, however warned the death toll was "very heavy in the ranks of the Nigerien army," without providing further details.

State television reported that Niger's President Mahamadou Issoufou had called a meeting of the national security council after the Islamists' attack.

Niger, along with Chad, Cameroon and Nigeria, has recently launched a joint offensive to end Boko Haram's six-year insurgency, which has claimed 13,000 lives and caused about 1.5 million people to flee their homes.