Twenty people were wounded on Thursday in northern Mali’s restive Kidal region, including 18 U.N. peacekeepers from Chad, in a rocket attack on a military base for U.N., French and Malian forces, a U.N. spokesman said.

Six of the peacekeepers from the MINUSMA mission were seriously wounded by the attack on the base in the town of Tessalit, spokesman Olivier Salgado told Reuters. He said it was unclear who was responsible.

France’s military said none of its soldiers were injured.

Kidal has been under the control of Tuareg rebels since an uprising in 2012, and tensions regularly flare between armed groups and the government.