U.N. spokeswoman Marie Okabe said only around half a dozen U.N. vehicles had been permitted to cross into Ethiopia, U.N. personnel had been threatened at gunpoint and the Eritrean company providing food to the peacekeepers told the United Nations it could no longer do so.
"Not more than six vehicles have been allowed by the Eritreans to cross into Ethiopia," she said, adding that peacekeepers trapped on the border between Eritrea and Ethiopia had only had a few days of emergency food rations.
She said the U.N. Security Council had been informed about the situation. The council's current president, Panamanian Ambassador Ricardo Alberto Arias, said the body would discuss the issue later on Friday.
The 1,700-strong U.N. mission started work in 2000, at the end of a two-year war between the two Horn of Africa neighbors that killed an estimated 70,000 people. They have been stationed in a 15.5-mile (25-km) buffer zone inside Eritrea, which has said it no longer wants U.N. troops in the country.
The two countries insist they will not start another war, but both have moved tens of thousands of troops to the border because of a dispute over their 620-mile (1,000 km) border.
U.N. officials have said their peacekeepers were reluctant to leave because they feared it could spark a new conflict.
"An emergency troop contributors' meeting is being called in the next few hours and the Eritrean authorities are being demarched also today at the highest level," Okabe said.
A demarche is an official diplomatic protest.