* Rebels kill colonel in charge of fighting insurgents
* Government says Ugandan rebel group responsible
* Many armed groups operate in mineral-rich east Congo
KINSHASA, Jan 2 (Reuters) - The colonel in charge of military operations against insurgents in eastern Democratic Republic of Congo was killed on Thursday in an ambush by the ADF-NALU, a Ugandan rebel group, the government said.
Colonel Mamadou Ndala, who helped to secure the military defeat of the powerful M23 rebel movement in November, died of his wounds after a rocket attack on his vehicle near the village of Mavivi in North Kivu province.
His killing highlighted the challenge facing the Congolese government and a 21,000-strong U.N. peacekeeping mission in their efforts to pacify dozens of armed groups operating in the mineral-rich east of the vast central African nation.
"Colonel Mamadou Ndala was killed in a ambush set by the ADF-NALU," said a government statement read on state television.
Ndala was in charge of tackling the ADF-NALU, which has stepped up its attacks in eastern Congo this year and has been identified by the U.N. mission as one of the main obstacles to peace.
The Allied Democratic Forces (ADF) emerged in the 1990s in opposition to the Ugandan government, allying itself with the National Army for the Liberation of Uganda (NALU). It was largely driven out of Uganda in the mid-2000s but has held out in eastern Congo.
Government spokesman Lambert Mende said three other soldiers in the vehicle were also killed in the attack. Ndala was travelling without a military escort, he said.
In the regional capital Goma, where many regarded the colonel as a hero for organising the defence of the town from the M23 rebels, residents flocked to his home, locals said. Traffic was thin and many shops closed their shutters amid fears of protests.
Millions of people have died in eastern Congo from violence, disease and hunger since the 1990s as foreign-backed insurgents have waged a series of rebellions, often for control of the region's rich deposits of gold, diamonds and tin.
ADF-NALU has been blamed for a spate of recent attacks and kidnappings around the town of Beni in North Kivu, including for the deaths of at least 60 civilians in two attacks last month. (Reporting by Bienvenu Bakumanya; Writing by Daniel Flynn; Editing by Mark Trevelyan)