DAKAR (Reuters) - Democratic Republic of Congo President Joseph Kabila pledged on Wednesday to restore order to the country’s restive Kasai region, where a worsening insurgency poses the most serious threat to his 16-year rule.

Slideshow ( 3 images )

Kabila’s failure to step down when his two-term mandate expired in December has further destabilized the loosely governed central African giant. Millions died in regional wars from 1996-2003 and dozens of armed groups still operate.

The Kamuina Nsapu insurrection erupted Kasai-Central province last August as a dispute over a customary chieftancy but has since spread to four other provinces, killing hundreds while taking on an increasingly political tone.

In a rare address to parliament, Kabila said he had designated Kasai an “operational sector” and called on militia members to lay down their arms.

“Confronted with these unacceptable atrocities committed against innocent victims ... we can no longer defer our responsibility to re-establish state authority in this part of the country by all possible legal means,” Kabila said.

The United Nations has accused both government forces and militia fighters of rights abuses and said it has credible reports that the army has carried out summary executions against suspected militants.

The government denies that its forces employ excessive force but has charged seven soldiers with crimes including for murder and mutilation in connection with a video that appears to show troops massacring suspected militia members.

The U.N. mission in Congo warned in a statement on Wednesday that an intensified military response “will only exacerbate the violence and further place the civilian population in danger”.

The mission also said this week that it has confirmed the presence of 23 mass grave sites in the region.

Under a deal struck with the opposition in December, Kabila can stay in office until after an election required to be held by the end of this year.

However, negotiations to implement the accord collapsed last week amid a disagreement over the procedure for nominating a new prime minister from the main opposition bloc.

Kabila said in his speech that if the impasse persisted, he would go ahead and name a prime minister in the next 48 hours, a move fiercely opposed by opposition leadership.