BBC's Paul Royall: The military position has changed

The move came in a letter to the United Nations Security Council, which had been holding an emergency session to discuss the border conflict between the two countries. Ethiopia has already accepted the peace plan.

Shortly after receiving the letter, the Security Council issued a statement welcoming the move and offered to provide all support to implement a peace agreement. Eritrea's offer follows a recent Ethiopian offensive in the disputed Badme region, which forced the Eritreans to retreat twice in as many days during fierce fighting.

The OAU's 11-point peace plan requires Eritrea to withdraw from Badme.

Rob Watson: The UN Security Council is taking this move very seriously

Until Saturday evening, the Eritreans had reserved their reply, asking for clarification on some points of the OAU proposal. But Eritrean presidential advisor Yermane Gebremeskol told the BBC that the current situation made the clarifications irrelevant.

The BBC's UN Correspondent, Rob Watson, says diplomats are saying privately that the Eritreans may have been persuaded to change tack because Ethiopia now appears to have the upper hand militarily.

Ethiopian offensive

After a brief lull, fighting resumed last Tuesday when Ethiopia launched its biggest offensive so far.

BBC's Alex Last reports from Asmara

Initially both sides claimed successes, but on Friday Eritrean authorities announced that Ethiopian forces, which outnumbers its own, had broken through at one point on the Badme front.

Details of the fighting are patchy as journalists are banned from the front-line but Ethiopian troops are reported to be strengthening their defensive positions after a series of successes.

Eritrean presidential adviser Yermane Gebremeskel said: "Eritrean forces are withdrawing to positions they are happy with."

Eritrean troops retreated a few kilometres on Friday after the Ethiopian breakthrough, but many decided to pull back again on Saturday to stronger positions, he said.

Diplomats in the region say that losses of both men and ressources have been very heavy on both sides.

Casualty count

On Saturday, Eritrean television announced that Eritrean troops had killed 9,000 Ethiopian soldiers, wounded 12,000 and captured 170 in three weeks of fighting in their border war, with "minimal" Eritrean losses.

The war over the ill-defined, largely uninhabited 1,000km (620-mile) border between the two Horn of Africa neighbours first flared last May but died down after about five weeks.

Subsequent diplomacy proved to be in vain, and the fighting resumed on 6 February, the starting point for the Eritrean casualty count.

Diplomatic row

Earlier this month, the Security Council adopted a resolution demanding an immediate ceasefire and a halt to arms sales to both countries.

Eritrea is complaining of its lack of representation on the OAU, which is based in the Ethiopian capital, Addis Ababa.

Since Ethiopia ousted the Eritrean ambassador on 9 February, Eritrea has had no representation at the OAU.

The OAU is trying to get Eritrea to reconsider a framework agreement to end the fighting.