NAIROBI, Oct 23 (Reuters) - Ethiopia's Ogaden National Liberation Front (ONLF) rebels said further fighting with security forces in the nation's remote east had brought the number of government soldiers killed to more than 250.

The Ethiopian government has been denying ONLF reports of mass casualties as falsehoods spread by their foreign-based supporters. No independent verification has been possible.

Facing several insurgencies in remote areas, Prime Minister Meles Zenawi's government has waged an unprecedented offensive against the ONLF after they killed 74 people during a raid on a Chinese-run oil exploration field earlier this year.

In its latest "military communique" on a flareup over the weekend, the ONLF said fighting continued on Sunday, a day after it reported killing 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," it said in the statement sent by email to foreign media on Tuesday.

"Thus far, 13 TPLF regime officers including a colonel and a captain have been killed in battles around Wardheer during the last two days. The ONLF has in its possession the military IDs of many of those officers."

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. ONLF casualties were "light given the scope of the engagements," it added.

Ethiopian officials were not immediately available for fresh comment on the latest ONLF statement on Tuesday.

During the year, both sides have variously reported hundreds of deaths, and accused the other of terrorising the population.

But with aid groups and journalist effectively barred from the worst-hit areas, independent checks on death-tolls have been impossible. A U.N. mission that went to the region in September did, however, call for a probe into reports of abuses.

Ethiopia accuses the ONLF, which is thought by analysts to number several thousand gunmen, of being terrorists supported by arch-foe and neighbour Eritrea.

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