* PM Abiy's forces have captured Tigrayan capital Mekelle
* TPLF says it is still 'fighting the invaders'
* Some fear protracted guerrilla war in northern region
* Nearly month-long war has destabilised east Africa (Adds Abiy comment, details, context)
ADDIS ABABA/NAIROBI, Nov 30 (Reuters) - The leader of rebel forces in northern Ethiopia said on Monday they were still fighting near the regional capital of Mekelle, which fell to government troops at the weekend after nearly a month of battles and air strikes.
"I'm close to Mekelle in Tigray fighting the invaders," Debretsion Gebremichael told Reuters in a text message, which the government dismissed as a deluded claim.
The war in Tigray region has killed hundreds and probably thousands, sent refugees into Sudan, enmeshed Eritrea, impeded a peacekeeping mission in Somalia, and heightened frictions between Ethiopia's myriad ethnic groups.
Prime Minister Abiy Ahmed's government launched an offensive on Nov. 4 against the Tigray People's Liberation Front (TPLF), accusing the ex-guerrilla movement, which dominated national government for nearly three decades until 2018, of insurrection.
Abiy's federal forces took Mekelle, a highland city of 500,000 people, at the weekend with relatively little resistance, though the TPLF later said it had shot down a plane and retaken one town.
TPLF leader Debretsion, a 57-year-old former radio operator, denied reports that he had fled to South Sudan and said his forces had captured some soldiers from neighbouring Eritrea around Wukro, about 50 km (30 miles) north of Mekelle.
Abiy's spokeswoman Billene Seyoum dismissed Debretsion's comments, saying: "The Federal government as a priority is busy governing a country and bringing stability to those affected. Tracking and responding to the many delusions of a disintegrating criminal clique that has become irrelevant is not our focus."
GUERRILLA WAR FEARED
There was no immediate comment from the Eritrean government, though at the start of the conflict it had denied involvement.
The TPLF has shelled Eritrea's capital Asmara.
Claims from all sides are difficult to verify since phone and internet links to Tigray have largely been down and access has been tightly controlled since the war began.
When he took office in 2018, Abiy pledged to unite Ethiopia's 115 million people, but there have been repeated bouts of bloody ethnic violence and hundreds of thousands have had to flee their homes.
Both sides have spoken of hundreds of dead in the Tigray war, and diplomats believe the toll is in the thousands.
Abiy told parliament on Monday that his troops had not killed a single civilian and were protecting Mekelle from damage. "We are not the (TPLF) junta. We have responsibilities. We conduct ourselves responsibly," he said.
Debretsion's defiant comments raise the spectre of a drawn-out guerrilla war. The battle-hardened TPLF helped to topple Ethiopia's Marxist dictatorship in 1991 and knows how to exploit its mountainous terrain and borders with Sudan and Eritrea.
Abiy won a Nobel Peace Prize last year for making peace with Eritrea, whose government also regards the TPLF as an enemy.
The U.S. State Department reported six explosions in Asmara on Saturday night, but without specifying the cause. Diplomats told Reuters they had been either rockets or missiles.
Ethiopia is a major contributor to an African Union peacekeeping force fighting al Qaeda-linked militants in Somalia, but has disarmed several hundred soldiers there of Tigrayan ethnicity, questioning their loyalty.
(Reporting by Addis Ababa newsroom, and Duncan Miriri and David Lewis in Nairobi; Writing by Andrew Cawthorne; Editing by Kevin Liffey)
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