However, Eritrea's information minister, Ali Abdu, said the troops had moved to the Temporary Security Zone (TSZ) to help harvest crops from state-run farms in the area, which, he said, constitutes one-third of Eritrean territory.
"It has nothing to do with the border issue. They [the troops] are involved in production and food security," he told IRIN.
The spokesman for UN Secretary-General Kofi Annan said the Eritrean Defence Forces had taken over one checkpoint manned by the United Nations Mission in Ethiopia and Eritrea (UNMEE), a peacekeeping force deployed in the TSZ.
"The Secretary-General is deeply concerned about the incursion into the zone," Stephane Dujarric, Annan's spokesman, said. "This development constitutes a major breach of the ceasefire and the integrity of the TSZ. It could seriously jeopardise the peace process and undermine the Algiers agreements between Ethiopia and Eritrea, with potential consequences for the wider region."
Annan urged Eritrea to withdraw its troops immediately from the TSZ and cooperate with the UN in restoring the ceasefire arrangement.
The TSZ was created under the 2000 cessation of hostilities deal signed in Algiers to end the 1998-2000 war over the border dispute between the two Horn of Africa countries.
Abdu repeated Eritrean complaints that Ethiopia was to blame for the continuing tension over the border because it refused to abide by the decision of an international border commission.
Both parties had initially undertaken to abide by the ruling of the border commission. However, when the commission announced its ruling in April 2002, Ethiopia rejected it because it awarded the border village of Badme, where the war started, to Eritrea. Ethiopia's rejection of the decision stalled the physical demarcation of the border in 2003.
In November 2004, Ethiopia's Prime Minister Meles Zenawi finally accepted the border commission's ruling "in principle" in a five-point peace proposal that called for a meeting with Eritrea to work out adjustments to the border on both sides.
Eritrea, however, has rejected calls for fresh talks. In the past year, there have been increased tensions along the frontier. Frustrated at the lack of progress in resolving the dispute, Eritrea banned UNMEE flights over its territory in October 2005 and expelled the peacekeeping mission's North American and European personnel.
Abdu said the reason soldiers were needed to do the harvesting was that many young people who should have been demobilised from the armed forces had to continue serving in the military because of the border tensions with Ethiopia, depriving the country of the civilian workforce that would otherwise be engaged in farming.
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This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information: https://shop.un.org/rights-permissions