"Four soldiers were also wounded and are receiving emergency care" after the incident Monday in the northeastern city of Malanville, the source told AFP, speaking on condition of anonymity as he was not authorised to discuss it.

The troops were part of Operation Mirador, launched in 2022 to secure Benin's borders amid a surge of jihadist violence in West Africa, the officer said.

Malanville sits on Benin's border with Niger, which has been rocked by attacks in recent years, as have nearby Sahel states Mali and Burkina Faso.

The oil pipeline connects the Agadem oil fields in southeastern Niger to the Benin coast.

Another operation in June killed seven soldiers in Benin in a national park on the Burkina Faso border.

Attacks in northern Benin have increased in recent years. The authorities accuse members of the Islamic State and Al-Qaeda groups based in neighbouring countries.

Benin's authorities rarely speak publicly on such offensives. In April 2023, they said there had been around 20 cross-border incursions since 2021.

Operation Mirador was launched the following year with 3,000 troops. Benin has recruited an additional 5,000 to reinforce security in the north.

The United States last month sent $6.6 million worth of armoured vehicles and defence equipment to Benin, while the European Union earlier this year announced 47 million euros ($49 million) in anti-terror funding for the country.

Neighbouring Ghana and Togo have also suffered jihadist attacks in recent years.