ADDIS ABABA - Ethiopia said on Friday it had no plans to invade arch-foe Eritrea, even as Asmara claimed for the fourth time in two weeks that Addis Ababa was preparing to launch an assault on the Red Sea state.

Tensions between the Horn of African neighbours have ratcheted up in recent weeks and now both nations are accused of moving troops closer to their disputed frontier.

"It should always be clear that Ethiopia does not have any reason or ambition to invade Eritrea other than protecting its sovereignty and peace," Information Minister Berhane Hailu told Reuters in Addis Ababa.

"If at all there existed anything new and any military movements around the Eritrea-Ethiopian border, it will be only the Eritrean government which shall be the cause of the problem and which shall take full responsibility," he said.

On Wednesday, U.N. Secretary-General Ban Ki-moon urged both nations to show "utmost restraint" as analysts warned of a possible repeat of a 1998-2000 border war that killed some 70,000 people.

In a statement posted online late on Thursday, Eritrea's Ministry of Information said deserting Ethiopian soldiers had told Eritrea they had been given orders to "prepare for war".

Both countries say they will not be the one to start any new war. They accuse each other of trying to provoke hostilities.

Ethiopia and Eritrea have been locked in a bitter dispute over their border since an independent boundary commission ruling in 2002 gave Eritrea the flashpoint town of Badme.

Frustrated by the lack of progress, last November the commission gave both sides one year to agree on the 1,000 km (620 mile) frontier, or it would set it on maps and let them mark it physically themselves.