"ONLF forces were warmly welcomed by the population in these areas and are administering medical care to those civilians killed by retreating Ethiopian occupation forces," the statement claimed.
The Ethiopian government has not responded to the statement.
Formed in 1984, the ONLF is fighting for the independence of ethnic Somalis in Ethiopia's oil-rich Ogaden region - which they say has been marginalised by the government in Addis Ababa.
The Ethiopian military launched a counter-offensive against ONLF rebels after they attacked a Chinese-run oil venture in Ogaden in April 2007, killing 74 people.
In April, Ethiopia said it had significantly weakened the the anti-government force, a claim ONLF rejects.