* ADF-NALU group based in eastern Congo since mid 2000s
* Congolese army launched offensive in December
* Mukulu has been helped to reach another country
By Elias Biryabarema
KAMPALA, April 22 (Reuters) - The leader of a Ugandan Islamist rebel group has fled his hideout in eastern Democratic Republic of Congo after a U.N.-backed offensive destroyed several camps belonging to his militia, Uganda's military said on Tuesday.
Jamil Mukulu, head of the ADF-NALU group, had escaped to another country, a Ugandan army spokesman said, weeks after the Congolese army said it was close to crushing the rebels with the support of U.N. forces and attack helicopters.
"We understand Jamil Mukulu is no longer in eastern Congo," spokesman Ronald Kakurungu told Reuters. "ADF started to feel pressure (and) some international allies evacuated him to another country."
ADF-NALU is an alliance of groups opposed to the Ugandan government that has operated from bases in the mountains of eastern Congo since being forced out of Uganda in the mid-2000s. It is believed to number up to 1,400 fighters.
The Islamist rebels have been blamed for kidnappings and attacks on civilians over the last year, including a Christmas Day assault near the town of Beni close to the Ugandan border that killed about 40 civilians.
Uganda worries that ADF-NALU, if left unchallenged in Congo's loosely governed east, poses a threat to its oil fields in the Albertine rift basin where Tullow Oil, Total and China's CNOOC are preparing for commercial production.
Congo's military launched an offensive against the group in December. Uganda has not participated in the operation, though a small contingent of Special Forces has helped provide the Congolese army with intelligence.
Defeating the ADF-NALU would mark the second major victory for Congo's army in less than a year after it routed the M23 rebel group in November.
Ugandan army spokesman Kakurungu did not say who had aided Mukulu, who faces U.N. sanctions, or to where he had fled.
He said troops had smashed seven ADF-NALU camps in the Virunga National Park, including Medina, Mukulu's headquarters, a three square mile military complex of fortified bunkers, observation posts, underground armouries and food gardens.
"The ADF has lost a large amount of weaponry. Their source of food is now no more, their supply lines were disrupted and their fighters are in disarray," he said. (Editing by Richard Lough and Rosalind Russell)