Secretary-General Kofi Annan has denounced Eritrea's decision to expel five U.N. security personnel and its arrest of a staff member with the U.N.'s peacekeeping mission there, his chief spokesman said. "The secretary-general urges the Eritrean authorities to rescind their decision on the U.N. personnel, release the detained UNMEE staff member, and provide urgent clarification on their actions," said a statement by Stephane Dujarric issued on Wednesday. The statement said the United Nations would investigate what it called "the unsubstantiated allegations". The United Nations Mission in Eritrea and Ethiopia (UNMEE) monitors the Horn of African neighbours' 620 mile (1,000 km) border amid continued tensions following their 1998-2000 war, which killed some 70,000 people, according to a report of Reuters.