Spokesman James Rubin said Lake, a former national security adviser to U.S. President Bill Clinton, would meet the leaders of the two countries as well as the head of the Organisation of African Unity (OAU), which is trying to mediate in the conflict.

``Mr. Lake will discuss modalities put forward by the Organisation of African Unity during the recent OAU summit in Algiers for implementing the framework agreement to bring peace to the region,'' Rubin told reporters.

As well as OAU Secretary General Salim Salim, Lake, who was leaving later on Wednesday, will meet Ethiopian Prime Minister Meles Zenawi and Eritrean President Isayas Afewerki.

Earlier this month the two East African neighbours and former allies both accepted an OAU peace plan that included a new round of mediation and withdrawal to positions held before the conflict started on May 6, 1998.

But on Wednesday Ethiopia accused Eritrea of rejecting the OAU peace plan and urged its people to redouble efforts to expel Eritrean forces.

The call appeared to further dampen the chances of a quick end to a conflict in which tens of thousands of soldiers have reportedly been killed in trench warfare and air strikes along a 600-mile (1,000 km) border between the two countries.

``We are supportive of the OAU's ideas and their framework, and (Lake) will be urging the two sides to work on that basis,'' Rubin said.

While approving the plan, Ethiopia also threatened to resume fighting if Eritrea continued to insist on preconditions and amendments before accepting the OAU plan.

"Ethiopia would be forced to take all the necessary steps to guarantee its sovereignty and territorial integrity if the Eritrean regime insists on its new preconditions and amendments," said the statement, published in the state-owned Amharic newspaper, Addis Zemen, and the Ethiopian Herald daily.

The details of the plan, worked out at an OAU summit in Algiers this month, differed very little from a draft OAU accord proposed in November.

Eritrea has accepted the plan, although it differs on the interpretation of some elements.

The 11-point plan calls for Eritrea to withdraw from the contested Badme region, the westernmost front along their 620-mile border. Eritrea captured Badme at the start of the war in May 1998, but Ethiopia has since recaptured it.

The agreement calls for both sides to then cease hostilities, and for international observers to deploy in the contested areas until a new border is demarcated.

The call appeared to further dampen the chances of a quick end to a conflict in which tens of thousands of soldiers have reportedly been killed in trench warfare and air strikes along a 1,000-km (600 mile) border between the two states.

Ethiopia and Eritrea both accepted this month an OAU peace plan which included a new round of mediation and withdrawal to positions held before the conflict started on May 6, 1998.

Ethiopia's Council of Ministers, chaired by Prime Minister Meles Zenawi, on Wednesday applauded the OAU resolution, passed at a summit in Algiers, and pledged to cooperate.

``Ethiopia for its part has accepted the Algiers proposals for a peaceful resolution of the conflict...But Eritrea has continued creating obstacles to the peace plan by presenting preconditions,'' the Council said.

``We therefore call on the patriotic defence forces and the Ethiopian people at large to remain steadfast and vigilant to protect the sovereignty and territorial integrity of the country,'' the Council added.

``Should Eritrea persist in the war, however, the Ethiopian government will take every action to regain its territory occupied by force,'' the Council added.

Even prior to the Algiers agreement both sides had accepted OAU plans to end the war, but this did not stop the fighting, in part because of disagreement over details and implementation.