Suspected Islamist militants attacked a U.N. base in the northern Mali town of Kidal with mortars and machine guns on Friday, killing three peacekeepers and wounding 30, United Nations and separatist sources said.

The attack is a fresh sign of instability in the desert region that is home to Islamist groups including al Qaeda in the Islamic Maghreb who have staged increasingly bold raids in recent months and have targeted the U.N. base several times.

“At about 7 a.m. (4 a.m. ET), the MINUSMA base in Kidal was the target of a complex attack which, according to provisional figures, caused the death of three blue helmets and around 30 wounded,” Mahamat Saleh Annadif, the Mali representative of the U.N. Secretary General, said in a statement.

Eight mortar shells were fired at the base and there was also gunfire, said Olivier Salgado, a spokesman for the U.N. peacekeeping mission, whose acronym is MINUSMA.

The base is part of an attempt by the United Nations to end violence in Mali following a takeover of the north by Islamists in 2012. A year later a French-led intervention force pushed the militants out of key towns in the region.

The U.N. mission has not stopped the violence and Islamist militants have expanded their attacks in recent months into other parts of Mali and beyond.

These have included an attack on a hotel in Mali’s capital Bamako in November, in which 20 people died, and one on Burkina Faso’s capital Ouagadougou in January, in which 30 were killed.

There is also a decades-long separatist struggle in northern Mali by ethnic Tuaregs.