United Nations officials say Eritrea has ordered the expulsion of Western staff members from the U.N. mission that monitors the tense border with Ethiopia.

The officials Wednesday said a letter from the Eritrean government gives U.S., Canadian, European and Russian staff members 10 days to leave. They say no reason was given.

Ethiopia immediately denounced the move as unhelpful to efforts aimed at calming fears of a new border war. The countries fought a border war from 1998 to 2000, killing 70,000 people.

Media reports say the order would affect about 160 military observers and civilian staff with the U.N. peacekeeping mission, which numbers about 3,500 people.

Diplomats suggest the move reflects Eritrea's unhappiness with the United Nations' handling of the border dispute. Last month, the Security Council threatened sanctions against Eritrea and Ethiopia if they use force to settle their border dispute.

Some information for this report provided by AFP, Reuters and AP.