The United Nations said Thursday that Ethiopian troops had occupied a demilitarized buffer zone set up to separate Ethiopian and Eritrean armies, but the soldiers left after U.N. peacekeepers intervened.

Ethiopian forces occupied the eastern sector of a temporary security zone for five days beginning Saturday, a spokeswoman for the U.N. Mission in Ethiopia and Eritrea said. There was no immediate comment from Ethiopia.

Meanwhile, Eritrea dismissed as a glaring example of big power bias a U.N. Security Council resolution threatening sanctions against it and Ethiopia if both countries failed to step back from the brink of war.

Eritrea, which has long said the West favors Ethiopia in its dealings in the region, said the council had risked worsening tensions by failing to punish Ethiopia for its refusal to honor a treaty that ended their war, which lasted from 1998 to 2000.

The resolution adopted by the council Wednesday called on Eritrea to end its restrictions on U.N. helicopter flights and other peacekeeping operations. It also told both sides to reduce the number of soldiers facing each other across the U.N.-enforced buffer zone.

The resolution expressed "grave concern" that Ethiopia had failed to fully accept the binding ruling of an international commission on the Horn of Africa countries' shared border.

"The Security Council has adopted another deplorable resolution," Eritrea said in a statement.

"This lopsided resolution underscores one glaring fact: It is not international law and the Charter of the United Nations that govern the conduct of the Security Council but sheer power politics and the narrow interests of major powers."

Nearly 3,300 U.N. peacekeepers monitor the buffer zone as part of the 2000 peace accord ending Ethiopia and Eritrea's border war, in which more than 70,000 people were killed.

Peacekeepers' movements have been restricted since Oct. 5, when Eritrea banned U.N. helicopter flights and other activities. That resulted in about 60 percent of the peacekeepers withdrawing, unable to do their work.

"The Ethiopian troops, which numbered about 20, said they entered into the TSZ because they were concerned after U.N. troops vacated the strategic location," the U.N. spokeswoman, Gail A. Bindley-Taylor-Sainte, told reporters.

She said the Ethiopian troops were stationed three miles from the Ethiopian border on the Bure-Bada road, considered by military experts to be a highly strategic position because of its high altitude.

Recent military maneuvers on both sides of the 567-mile frontier have fueled fears that the war will resume.