(Reuters) - Ethiopia has rejected a claim by a rebel group that it has taken control of a gas field in the country's Ogaden region being explored by Malaysian state oil company Petronas.

Firms including Petronas and Vancouver-based Africa Oil Corporation are exploring the Ogaden for potential oil and gas reserves.

The Ogaden National Liberation Front (ONLF), a group that wants more autonomy for the region, regularly warns foreign firms to leave the area's deserts. Commercial amounts of oil and gas have not yet been extracted.

"Special forces of the Ogaden National Liberation Front yesterday liberated and are now in control of the Hilala field in Eastern Ogaden," the rebels said in a statement.

"Troops of the regime abandoned the field after being surrounded by our forces and determining their chances for survival were slim," the group said late on Saturday.

The Ethiopian government head of information, Bereket Simon, told Reuters the statement from the insurgent group was "a complete lie."

"This is a well-protected area, no force could take it over, let alone the ONLF who we have driven to total disarray," Bereket said. "They're simply fabricating stories and trying to live on in the media. They just want to create news."

The government says the Hilala field and the nearby Calub field, together covering 350,000 sq km, are believed to have gas reserves of 4 trillion cubic feet. Petronas has been working on both sites since 2007.

BRITON KILLED

A British geologist was shot dead last month in the Ogaden while working for IMC Geophysics International, subcontracted to Petronas. The ONLF denied involvement and the government said "bandits" were responsible.

Local media and the ONLF said the Malaysian firm has recently suspended operations in the Ogaden region.

"If this is the case, Petronas has chosen wisely and this decision will not be forgotten," the ONLF said.

The company could not immediately be reached for comment.

Ethiopian forces launched an assault against the ONLF -- who have been fighting for more than 20 years -- after a 2007 attack on an oil exploration field owned by a subsidiary of China's Sinopec Corp, Asia's biggest refiner.

Analysts say the rebels are incapable of ousting the government but can hamper development and weaken security forces in the Ogaden with hit-and-run attacks.

The government this month told Reuters its allied-militias in the region had been attacked by the ONLF.

In November, the group said it had captured seven towns in the region and killed almost 1,000 Ethiopian troops and government-allied militiamen. The government confirmed the rebel assault but Prime Minister Meles Zenawi said they had been "crushed."

(Editing by David Clarke and Elizabeth Fullerton) - Reuters