* Congo intervention unit will be several thousand strong
* New Security Council resolution needed to approve unit
* UN experts accuse Rwanda of backing nine-month insurgency
UNITED NATIONS, Jan 25 (Reuters) - U.N. Secretary-General Ban Ki-moon will recommend to the U.N. Security Council that a peace enforcement unit be deployed in eastern Democratic Republic of Congo to take on the M23 rebels and other armed groups, a senior U.N. official said on Friday.
The intervention unit of a few thousand troops would aim to prevent armed groups from expanding territory in the resource-rich region by overpowering and disarming them. The unit would be contained within the existing U.N. force, known as MONUSCO.
"It is not simply peacekeeping, this is peace enforcement. It's a much more robust stance," said the official, who declined to be named. "It will be a deterrent against the armed groups."
Diplomats and U.N. officials say that peace enforcement missions allow the use of lethal force in serious combat situations, while peacekeeping operations are intended to support and monitor an already existing ceasefire.
The Congolese army has failed to quell a growing nine-month insurgency by M23, which has dragged Congo's eastern region back toward war and has received cross-border support from Rwanda and Uganda, according to independent U.N. experts. Both governments strongly deny the accusations.
MONUSCO, which has a mandate to protect civilians, suffered a severe blow to its image after it chose not to intervene as well-armed M23 rebels seized control of the eastern city of Goma in November. The rebels withdrew after 11 days.
A peace enforcement brigade within MONUSCO would be able to quickly respond to such operations by armed groups in the future and the official said it was hoped that the force could be on the ground in three months.
The official said one battalion already operating within MONUSCO would become part of the intervention unit along with two new battalions. The new troops would not increase the total MONUSCO force beyond its authorized mandate of about 22,000.
But a new Security Council resolution will be needed to approve the peace enforcement unit. The official said the 15-member council was likely to agree to the intervention brigade.
South Africa and Tanzania are among the countries that have been considered possible providers of troops for the peace enforcement wing of MONUSCO, Security Council diplomats say.
The decision to create an enforcement wing of MONUSCO came in response to a call from African nations for the deployment of a neutral international force to deal with the rebel threat in eastern Congo.
The 15-member Security Council gave a green light this week for peacekeepers to use surveillance drones in eastern Congo after weeks of delay over concerns among Russia, China and Rwanda about the use of aerial spy equipment.
Despite Rwanda's alleged involvement in the M23 rebellion, the official said any concerns it might have over the creation of an intervention unit would be allayed by the fact that the troops would be targeting not just M23 but all armed groups, including the FDLR rebel group.
Rwanda - which began a two-year term as a council member this month - has in the past cited the presence of the FDLR, or Democratic Forces for the Liberation of Rwanda, as a reason for sending troops into neighboring Congo.
The last U.N.-led peace enforcement mission approved by the Security Council was in Somalia in the early 1990s when 18 U.S. troops were killed in the "Black Hawk Down" incident, an event that led to U.S. withdrawal of combat troops from U.N.-commanded peacekeeping operations.
Ban will recommend the intervention force to the council in a report early next month after a regional political deal is signed by leaders on the sidelines of the African Union summit on Monday, the official said.
The deal - to be signed by Democratic Republic of Congo, Rwanda, Uganda, South Africa, Burundi, Congo, Angola and Tanzania in Addis Ababa - will also refer to a strengthening of the MONUSCO force, said the official.
"The leaders of the region commit to work together and to address the underlying issues, whether it's economic, military, political," the official said.
The leaders of those eight states will meet twice a year on the sidelines of the African Union summit and the U.N. General Assembly, he said. Ban or his Great Lakes special envoy - who is yet to be appointed - would also attend and oversee the process. (Editing by Eric Walsh)