Eritrea has ordered five United Nations staff to leave the country within 24 hours, Eritrean state radio reports.
Eritrea has imposed restrictions on the UN's operations
The reports said the five officials had been engaged in espionage, using radio communications and employing spies.
The broadcast claimed that a number of UN peacekeepers were last week caught attempting to smuggle Eritreans out of the country.
The UN has heard the report, but is still investigating the situation, a spokesman told the BBC.
The staff named in the Eritrean radio report are from the UK, New Zealand, South Africa, Liberia and Trinidad and Tobago.
Dec 2000: Peace agreement
Apr 2002: Border ruling
Mar 2003: Ethiopian complaint over Badme rejected
Sep 2003: Ethiopia asks for new ruling
Feb 2005: UN concern at military build-up
Oct 2005: Eritrea restricts peacekeepers' activities
Nov 2005: UN sanctions threat if no compliance with 2000 deal
The UN has more than 2,000 staff patrolling a buffer zone on the Eritrean side of the disputed Eritrea-Ethiopian border.
The UN deployment is part of a peace deal signed by the two countries in 2000 to end a two-year border war.
Since last year, Eritrea has placed restrictions on the UN operation, in response to Ethiopia's failure to withdraw from the disputed town of Badme, which an international arbitration commission awarded to Eritrea.