ASMARA, Eritrea (AP) _ Eritrean forces claimed to have dealt the Ethiopian army a heavy blow on a new front Monday, inflicting casualties and forcing thousands of soldiers to retreat.

Ethiopian officials, meanwhile, admitted that jet fighters were being used to support a counteroffensive. Eritrea condemned the violation of a moratorium on airstrikes that was brokered last June by President Clinton.

Fighting over the weekend ended an eight-month stalemate in the war between the two Horn of Africa nations. Disagreement over their unmarked border has simmered since Eritrea gained independence from Ethiopia in 1993.

Both countries have accused the other of setting off the latest round of fighting along the 600-mile border.

Eritrean spokesman Yemane Gebremeskel said fighting around Tserona, 60 miles south of the Eritrean capital of Asmara, lasted most of the day after Ethiopia attacked there for the first time Monday.

``Large parts of (Ethiopia's) 20th and 24th divisions _ which are supposed to be their elite fighters _ have been severely battered,'' he told The Associated Press.

The two sides also fought for a third day at two other fronts, including Badme-Shiraro, the origin of the border dispute. The village of Badme, 95 miles southwest of Asmara, burned Monday under fierce shelling and Ethiopian machine-gun fire.

An Ethiopian helicopter gunship fired on Eritrean positions Monday in the arid, dusty mountains.

The bodies of several Ethiopian soldiers lay strewn about the battlefield.

At least one dead Eritrean soldier lay in a trench. The wounded, limping and bandaged, were carried off by trucks after dark, when the shelling subsided.

On the outskirts of Asmara, officials also showed reporters about 100 Ethiopian prisoners captured on the Badme-Shiraro front, where the fighting first broke out on Saturday.

The Ethiopian POWs, speaking in front of their captors, said their commanders forced them to march overnight Friday and attack Eritrean positions early Saturday morning.

The Ethiopians said they were overwhelmed and after eight hours of battle were ordered to retreat. Instead they surrendered.

At the United Nations, spokesman Fred Eckhard said U.N. envoy Mohamed Sahnoun was flying to New York on Monday to brief the secretary-general and the Security Council on his peace mission.

The Organization of African Unity urged both countries to end fighting immediately Monday and recommit themselves to a peaceful solution to the crisis.

The border dispute turned violent in May, when both sides began exchanging artillery fire and airstrikes near Badme. More than 1,000 people were killed on both sides.