Ethiopian armed forced have attacked rebel bases inside Eritrea, accusing its neighbour of training fighters who have carried out border raids, including a January attack that killed five tourists.
Thursday's attack was the first offensive by Ethiopian troops inside Eritrea since the end of a 1998-2000 war that killed 70,000 people and still festers. The frontier dispute that ignited the conflict remains unresolved.
Ethiopia routinely accuses Eritrea of supporting Ethiopian separatist groups.
Ethiopia has blamed an Eritrea-based rebel group for the kidnapping of Westerners in its northern Afar region in 2007, and again for attack in the same area in January.
"Our national defence force has today taken measures against military posts inside Eritrea in which subversive and anti-peace elements were trained," Shimeles Kemal, a government spokesman, told the media.
Gunmen killed two Germans, two Hungarians and an Austrian in an attack on a group of tourists in the remote Afar region on January 17, and seized two Germans and two Ethiopians.
The rebel group in the Afar region said last week it had freed the two German tourists, although there has been no official confirmation of the release.
"These groups are operating in the Afar area. We know for certain that the Eritrean government harbours, supports, trains and deploys subversive groups that occasionally launch attacks on civilian and infrastructure targets inside Ethiopia," Kemal said.
He added that Ethiopian soldiers attacked three places, Ramid, Gelahbe and Gimbi, an estimated 16km inside southeastern Eritrea.
"We will continue our measures as long as they remain a launching pad for similar attacks," he said.