The United Nations has protested to Eritrea over the arrest of 13 local staff members employed to monitor the disputed border with Ethiopia.
Tensions along the border are mounting
Another 30 staff are in hiding, in fear of being detained as well.
No official reason has been give for the arrests, but the information minister said he would not allow the UN to give sanctuary to "fugitives".
Recently Eritrea has clamped down on UN operations, in retaliation for the failure to implement a border ruling.
The neighbours fought a brutal war between 1997-2000 which ended with a peace agreement committing both sides to abide by the ruling of an independent commission which demarcated the boundary.
However, Ethiopia has not withdrawn its troops from the disputed border town of Badme, which the commission awarded to Eritrea.
Eritrea wants the international community to put more pressure on Ethiopia to comply with the ruling.
Last year, Eritrea banned UN helicopter flights and called for the expulsion of Western peacekeepers.
Then in January, Eritrea's President Isaias Afewerki refused to allow the team of US diplomats and army officials to visit the border area.
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
Talking about the weekend detentions, Eritrean Information Minister Ali Abdu said if any person broke the law they were subject to the law, regardless of where they worked.
"We will not allow Unmee to be a sanctuary for fugitives," he said.
The UN Security Council has delayed a decision until March on the future of its peacekeeping troops in the region, pending US efforts to resolve the impasse.
It may scale down the peacekeeping force which currently separates thousands of troops from the two countries who are deployed close to the border, raising fears of renewed conflict.
UN head Kofi Annan reported back in January to the Security Council on resolution 1640, which carries the threat of sanctions against both countries if they do not withdraw troops they had sent to the border.
He presented them with six options, from leaving things as they are to pulling out.