Four United Nations peacekeepers were killed and five wounded in central Mali on Wednesday after a convoy struck an explosive device and came under fire, the U.N. said.

It was not clear who carried out the attack about 20 km (12 miles) north of the town of Bambara-Maoudé in the Timbuktu region.

Islamist groups linked to al Qaeda and Islamic State operate in the region and have made much of the West African country ungovernable.

The U.N. mission in Mali, known as MINUSMA, said in a statement on Wednesday that three peacekeepers had been killed and six wounded in the attack. A MINUSMA spokesman said on Thursday that a fourth had since died.

The dead peacekeepers were from Ivory Coast, the country’s defence ministry said in a statement.

MINUSMA has over 13,000 troops to contain violence caused by armed groups in the north and centre of the country. The mission has recorded about 230 fatalities since 2013, making it the deadliest of the U.N.’s more than dozen peacekeeping missions.