Ethiopia's Ogaden National Liberation Front (ONLF) rebels has claimed fighting with security forces in the remote east had brought the number of government soldiers killed to more than 250.
The Ethiopian government has denied ONLF reports of mass casualties as falsehoods spread by their foreign-based supporters.
Facing several insurgencies in remote areas, Prime Minister Meles Zenawi's government has waged an offensive against the ONLF after they killed 74 people during a raid on a Chinese-run oil exploration field earlier this year.
The ONLF said fresh fighting had broken out at the weekend and that it had killed 140 government soldiers in an attack targeting a visiting senior official.
"Battles continued for a second day . . . in Ogaden, with TPLF regime [government] casualties rising to over 250 killed and an unconfirmed number wounded," the rebels claimed.
The group, which wants more autonomy in its arid region on the border with Somalia, said it had also destroyed 12 military vehicles during a counter-offensive that 1,500 government troops mounted in response to Saturday's rebel attack.
The ONLF said it had surrounded a large number of Ethiopian troops and urged them to surrender.