* Government troops kick off operations against ADF-NALU rebels
* Islamist force long seen as next target for U.N.-backed army
By Kenny Katombe and Chrispin Mvano
BENI, Democratic Republic of Congo, Jan 17 (Reuters) - D emocratic Republic of Congo forces attacked Ugandan Islamist rebels in the lawless east on Friday, launching a U.N.-backed offensive to clear insurgents from the mineral-rich zone.
Reuters correspondents outside the town of Beni, in North Kivu province, heard heavy gunfire as government troops moved in on positions held by ADF-NALU rebels who have been based in Congo for years and are seen as a major obstacle to peace.
Another rebel movement, M23, that had operated to the south of Beni was defeated late last year, highlighting how Kinshasa and U.N. forces have begun to take the fight to gunmen that have plagued eastern Congo for nearly two decades.
"The Congolese army has launched operations against ADF-NALU in Beni and as usual (U.N. troops) will support the army to neutralize these rebels, who have been very active recently in this zone," said U.N. forces spokesman Colonel Felix Basse.
A Reuters reporter said that Tanzanian troops from a specialist U.N. "Intervention Brigade", which is mandated to go after Congolese rebel groups, had deployed near Beni but it was unclear if they had joined the fighting.
ADF-NALU is an alliance of groups opposed to the Ugandan government that has operated from bases in eastern Congo since the mid-2000s, undermining Kinshasa's grip on the area and handing Uganda a pretext for intervening there.
Earlier this week, Ugandan and Congolese army officers held a high-level planning meeting in Beni but Ugandan officials were not immediately available for comment on Friday.
Kampala has previously said it would share intelligence and capture fleeing rebels but not intervene directly in operations on the ground in Congo.
Congo and Uganda have long had rocky relations and U.N. experts have accused Kampala and fellow neighbour Rwanda of backing M23. Both nations denied the charges.
ADF-NALU has been blamed for a spate of recent attacks and kidnappings around Beni, including the deaths of some 40 civilians in an attack on Christmas Day.
The rebel group is believed to number up to 1,400 fighters and has abducted about 300 Congolese civilians over the past year, according to a U.N. report.
Having helped the Congolese army vanquish M23, the 3,000-strong U.N. Intervention Brigade had been widely expected to turn its attention on ADF-NALU and Rwandan Hutu FDLR rebels who are also roaming Congo's east.
The Ugandan government has said ADF-NALU is allied with Somalia's al Qaeda-linked al Shabaab movement but analysts say the nature of these ties is not clear, despite the ADF-NALU's clear Islamist ideology. (Additional reporting by Pete Jones in Kinshasa; Editing by David Lewis and Mark Heinrich)