YAOUNDE (Reuters) – Four soldiers and a senior government official were killed in Cameroon’s restive North West Region on Wednesday after their vehicle hit an improvised explosive device, according to an internal security note and another senior official.

The vehicle was traveling in a military convoy when it was ambushed by armed secessionists, the note seen by Reuters said, adding that five others were severely wounded.

The senior official said the five-vehicle convoy was returning to the town of Mbengwi, 450 km (279.62 miles) northwest of the capital Yaounde, after the installation of recently appointed local officials when the blast occurred.

No one has claimed responsibility for the attack.

It is rare but not unheard of for separatists in the conflict to use makeshift bombs, but Wednesday’s attack was among the deadliest since a June 2019 attack that killed four police officers and wounded six.

The security note said the powerful device was made up of large gas cylinders.

What began as peaceful protests in Cameroon’s two English-speaking regions in 2016 has degenerated into a violent insurgency pitting several separatist groups against Cameroon’s mostly French-speaking government.

More than 3,000 people have been killed and nearly a million displaced since 2017, with both sides regularly accused of committing atrocities.