Seven children are reported to have been killed by an improvised bomb in Togo.

Witnesses said they were woken by a loud blast late on Saturday in the Savanes region, in the north of the country.

"An investigation is ongoing to determine the circumstances of this explosion and identify the perpetrators," the army is quoted as saying in a statement on Sunday.

Islamist militants linked to Islamic State and al-Qaeda have attacked numerous targets in a string of countries in the Sahel.

The Togolese army has been on high alert following the country's first deadly militant attack in May, when eight soldiers were killed near the border with Burkina Faso.

Togo last month declared a state of emergency in its northern region following the attack.