But Ethiopia's latest offensive, now 10 days old, has opened up the war, capturing Eritrean positions on the western front and dramatically tipping the balance along the disputed 1,000 km (600 miles) border.

Eritrea's army, which prided itself on the apparent invulnerability of its heavily fortified trenches, was forced to retreat when Ethiopian forces poured across the western Badme front only hours into the offensive on May 12.

As trench war gave way to running battles, the Ethiopians chased enemy troops deep into Eritrean territory. They took a string of bombed-out villages and then seized Barentu, a large town that served as Eritrea's key command and logistics base for the entire front.

Burned-out tanks and rotting corpses lie on the plains and mountain roads around Barentu, the remnants of raging battles as the Ethiopians surged northwards.

The speedy assault has left Ethiopia in command of a large chunk of Eritrean territory -- for the first time since the border war began -- and a clear upper hand.

It appeared to take Eritrea by complete surprise. But Ethiopian military officers say they were confident of success once they penetrated Eritrea's first line of defence.

``It is always tougher to break the trenches,'' said Colonel Gebre Kidane, a senior military commander in the west. ``Then it gets easier as you go along.''

But Ethiopia now has to decide where it wants to go next.

TALKS, OR MORE WAR?

It continues to chase retreating Eritrean troops up through western Eritrea towards the town of Agordat -- raising speculation that the capital, Asmara, could be a target. Already the United States and Britain have advised their citizens to leave.

Ethiopian troops are also moving east towards the central war front, where Eritrean forces still occupy the disputed border town of Zalambessa.

Eritrea says its forces are reinforcing around Mendefera, a key town on the main supply route from Asmara to the central front. But Ethiopian air attacks are moving closer to Asmara.

Ethiopia says its air force bombed and destroyed an anti-aircraft missile site near Mendefera on Saturday.

If Ethiopia were to take Mendefera, it could attack Eritrean forces around Zalambessa from the front and rear. But it could then be targeted by Eritrea's army from two sides.

Few doubt that such a battle would be among the bloodiest in a war that has already killed tens of thousands of soldiers.

``It is extremely important the fighting is stopped before it spreads to the other fronts,'' said a Western diplomat in Addis Ababa, adding that he hoped Ethiopia would now offer peace talks from a position of strength.

U.N. agencies say hundreds of thousands of civilians have already been forced to flee by the recent fighting, thousands of them across the border into neighbouring Sudan.

The U.N. Security Council had tried to persuade Ethiopia and Eritrea to reopen peace talks in the days before the latest offensive began. It has now declared an arms embargo on both countries.

Ethiopia paid no attention, convinced it had a better chance of ending the war on the battlefield than at the negotiating table.

Ethiopia insists it has no plans for a long-term occupation of Eritrea -- an Ethiopian province before winning its independence in 1993 -- but says it wants to make sure the enemy army can pose no future threat.

It also hopes a military collapse would endanger the rule of Eritrean President Isayas Afewerki, although there is little organised opposition against him in Eritrea.

``While Isayas is in power, there will be no peace,'' Ethiopian government spokesman Haile Kiros said.

``We will go all the way until we liberate our territory. Then it is up to the Eritrean people to decide what to do with their arrogant government,'' he said.