DR Congo has asked the spokesman of the UN's peacekeeping mission in the country to leave "as soon as possible", according to an official letter seen by AFP on Wednesday.

The central African nation's government asked the peacekeeping mission, known as MONUSCO, to withdraw spokesman Mathias Gillmann over "indelicate and inappropriate remarks" he made, the letter said.

"The government would very much appreciate that action be taken for Mr. Mathias Gillmann to leave Congolese territory as soon as possible," it added, citing recent tensions between the peacekeeping mission and locals.

Protests against MONUSCO erupted in parts of eastern Congo last week, leading to the death of 36 people including four UN peacekeepers.

Anger has been fuelled by perceptions that MONUSCO is failing to do enough to stop decades of armed conflict in the region.

More than 120 militias operate in the Democratic Republic of Congo's troubled east, where civilian massacres remain common.

The government letter to MONUSCO, dated July 28, did not provide details about Gillmann's remarks.

But a senior government official who asked for anonymity said the spokesman had told French radio station RFI that UN peacekeepers did not have the military means to defeat a notorious armed group called the M23.

The militia had lain mostly dormant for years before resuming fighting last November.

It has since made significant gains, capturing the strategic town of Bunagana on the border with Uganda last month.

The group's resurgence has also damaged diplomatic relations between the DRC and its smaller neighbour Rwanda, which the Congolese government accuses of backing the M23.

The United Nations first deployed an observer mission to eastern Congo in 1999 and established MONUSCO in 2010 with a mandate to conduct offensive operations.

The peacekeeping operation is one of the largest and costliest in the world, with an annual budget of around a billion dollars.