The attack, which took place on Monday, was the fifth in the country since last year, as jihadist groups operating in the Sahel appear to be gradually heading towards coastal West Africa.

"At around 22:00 GMT, security forces from operation Koundjoare were once again victim of a complex attack involving an improvised explosive device on one of our patrols in the village of Blamonga," said Lieutenant-Colonel Samah Soussou, a defence spokesman in an interview with the private radio station Kanal FM.

"Members of the terrorist armed groups opened fire. Our soldiers, who are brave and determined, fired back vigorously, forcing the enemy to retreat," said Soussou.

"Unfortunately, we have recorded several injured who are being taken care of," he added, without giving further details.

The official said that the militants retreated to Burkina Faso, making it difficult to pursue them across the border.

But a clearance operation is ongoing on the Togolese side, he added.

The country declared a state of emergency earlier this year in its far northern provinces to allow security forces more flexibility to operate.

Eight soldiers were killed in May in an assault claimed by a Mali-based alliance of Al-Qaeda affiliated jihadists.

Gunmen also clashed with Togo troops outside a military post in Goulingoushi area in June, before they were forced back across the border.

The deadliest attack was in July, when gunmen attacked four northern villages.

The government has not confirmed a death toll but local media said at least 15 people were killed in that attack.