Building on a string of successful military advances on the western end of the border last week, Ethiopian forces pounded Eritrean lines from early morning and army chiefs said they quickly broke through.

``They have already shattered the defence lines of the enemy, they have overrun many of their trenches by flanking from the right and the left, finding gaps and penetrating deep in,'' said Seyoum Mesfin, Ethiopia's foreign minister.

There was no immediate reaction from Eritrean authorities on the claims. Tens of thousands of Eritreans have, however, crossed into Sudan as refugees to escape the fighting, Sudanese officials said.

A new offensive for control of the central front -- focused on and around the Eritrean-occupied town of Zalambessa -- appeared inevitable after Ethiopia's recent gains in the west.

The fight for Zalambessa, involving tens of thousands of soldiers, had been billed as the decisive battle of the two- year-old conflict and Ethiopian Prime Minister Meles Zenawi told diplomats on Tuesday the war could be won within days.

One military analyst said he had no doubt about Ethiopian resolve. ``The Ethiopians have got their death masks on,'' he said.

Eritrea seized land all along the Zalambessa front at the start of the war in May 1998 and, firmly entrenched on high mountain ridges, beat back all previous Ethiopian assaults.

But after pushing deep into western Eritrea last week, Ethiopian forces began moving east, apparently threatening the strategic town of Mendefera, about 30 miles (50 km) in from the Zalambessa front on the road to the capital Asmara.

Military analysts had expected the key battle to take place at Areza, a small town on an escarpment high above Mendefera, and Eritrea reinforced its positions there.

But the Ethiopian attack finally came on the border itself.

``Eritrea was anticipating facing Ethiopian troops along the Areza front,'' Seyoum said. ``This is not what happened. It was an absolute surprise for them.''

FIGHTING OVERSHADOWS PEACE EFFORTS

It also appeared to strike a blow at diplomatic efforts to end the fighting and reopen peace talks.

Special envoys from the European Union and the Organisation of African Unity met with both sides for a second day on Tuesday in a new round of shuttle diplomacy aimed at bringing both sides back to the negotiating table.

Eritrea said it would attend a new round of talks without preconditions while Ethiopia said it was also happy to reopen talks but insisted the war would go on regardless.

``We shall negotiate while fighting. We shall fight while negotiating,'' Meles said. ``Whichever road leads to peace quickly will be the road we follow.''

His government says peace talks are not incompatible with a sharp escalation of the fighting because both could serve to end the war by forcing Eritrea to pull out of the disputed territories it still occupies.

More ominously, Ethiopia says it is convinced Eritrean President Isayas Afewerki will only give up when his armed forces are completely destroyed.

Seyoum said on Tuesday the Ethiopian army would not hesitate to go as far as it needs to.

``Until Eritrea is out of each and every square inch of Ethiopian territory, we will pursue this war,'' he said.

He stressed, however, that Ethiopia would pull out of the Eritrean territory it now controls as soon as it wins the war.

``We are reassuring the Eritrean people that we have no designs to humiliate Eritrea, or annex Eritrean territory, or erase Eritrea from the map.''

Eritrea was for long a province of Ethiopia but won its independence in 1993 after a long guerrilla war against the former Marxist dictatorship of Mengistu Haile Mariam.

The U.S. and British governments have advised their nationals to leave Asmara and many commercial flights to and from the capital city have been cancelled.