Ethiopian Prime Minister Meles Zenawi has accused Eritrea of reinforcing troops in the tense buffer zone along their border in recent days but said it was "not a new phenomenon".
Fears of renewed conflict between the neighbours, who fought a two-year border war, have intensified after Eritrea banned UN helicopter flights over a 25 km-wide temporary security zone (TSZ) along the 1,000 km-long (620 mile) frontier.
The move, which reduces the United Nations' ability to monitor troop movements, prompted U.N. Secretary-General Kofi Annan to warn on Monday that the United Nations might end its peacekeeping mission if Eritrea maintained its flight ban.
Eritrean officials were not immediately available for comment.
UN officials say they have seen no significant military changes on the ground. However, the helicopter restrictions prevent monitoring of more than 55 percent of the border region.
UN peacekeeping officials have cut staff in 18 of the 40 border posts beause they can no longer ferry supplies to them.