* New M18 rebels clash with militias in northeast Congo
* Some 10,000 refugees enter Uganda's West Nile region
* Uganda fears rebels pose danger to its oil-rich region
* M18 leaders unknown but apparently not linked to M23
About 10,000 Congolese refugees have fled into Uganda to escape fighting between a new rebel faction identified as M18 and militias in Congo's lawless northeast, Red Cross and military officials said on Monday.
The Ugandan military says M18 is not linked to the M23 insurgency battling the U.N.-backed Democratic Republic of Congo's armed forces in nearby North Kivu province and that the leadership of the new rebels remains unknown.
Rich in lucrative minerals and agricultural commodities but long poorly governed, eastern Congo has spawned various rebel and militia groups over the past few decades, some formed mainly to seize the region's abundant natural resources.
Uganda Red Cross spokeswoman Catherine Ntabadde said refugees began flowing the Koboko district in Uganda's West Nile region in the past couple of days from the Ituri area of Congo's Orientale province where the M18 is fighting.
"An estimated 10,000 refugees have crossed into Koboko district from the Democratic Republic of Congo but the number could grow... we're now working together with partners to assess their needs and how to resettle them."
The West Nile region forms part of Uganda's Albertine rift basin where the East African state has discovered an estimated 3.5 billion barrels worth of crude oil reserves.
"We know that M18 is a new rebel group in Orientale Province and they've been clashing with some militias there and forcing people to flee," said Lieutenant Colonel Paddy Ankunda, Uganda's military spokesman.
"But we don't know their leadership yet or what they want ... We are still trying to learn those details."
It is not clear what the M18 name stands for. The M23 rebels are named after a March 23, 2009 peace deal that ended four years of insurrection. Fighting resumed 20 months ago after M23 accused Kinshasa of reneging on the deal, including a pledge to integrate rebels into the armed forces.
Ankunda also did not say who the "militias" were. But they are often local citizens who take up arms to defend their communities from other groups in the lawless region, or may be a breakaway faction of a rebel movement.
Ankunda said the Ugandan army was helping humanitarian workers check the refugees to ensure there are no members of the Allied Democratic Forces trying to enter in disguise.
ADF, which claims links to al Qaeda, operated in the 1990s from bases in the Ruwenzori Mountains and across the frontier in the eastern Congo jungle. Uganda's military says ADF remains a threat to Ugandan oil fields around Lake Albert.
In the M23 conflict, which has displaced tens of thousands of people, government forces said they took the rebel redoubt of Rutshuru on Sunday in a third day of fierce battles in which one U.N. peacekeeper was killed and another injured.
After two months of relative calm, fighting flared on Friday after peace talks in neighbouring Uganda broke down when M23 rebels demanded a full amnesty for their leaders. President Joseph Kabila last week ruled out a blanket pardon.