The US has condemned Eritrea for "military aggression" after deadly clashes on the border with Djibouti.
The US state department said it understood nine Djiboutians had been killed and more than 60 injured in the clashes, which began on Tuesday.
Eritrea's government denied hostile intentions towards its neighbour.
Meanwhile, Djibouti's President Ismail Omar Guelleh has said his country would "valiantly defend its territorial integrity by all means".
After weeks of tension, fighting broke out on Tuesday in the Mount Gabla area, also known as Ras Doumeira.
The clashes continued into Wednesday.
The US and France, which both have military bases in Djibouti, called for an end to the violence.
"We call on both sides to cease all military hostilities immediately and to reduce tensions by withdrawing troops from the border area," US state department spokesman Gonzalo Gallegos said.
"The United States calls on Eritrea and Djibouti to move forward at once to resolve border issues peacefully, in accordance with international law, and for Eritrea to accept offers of third-party mediation."
The French foreign ministry has said it is highly concerned about the border clashes.
Djibouti said its forces were forced to fight back after coming under fire from Eritrean troops demanding the return of deserters who had fled to Djibouti.
But the Eritrean foreign ministry said that it "would under no circumstances get involved in an invitation of squabbles and acts of hostility designed to undermine good-neighbourliness".
Since Eritrea gained independence in 1993, the Horn of Africa country has been involved in two serious conflicts over territory with its neighbours.
Last month, Djibouti complained to the UN that Eritrea was fortifying its side of the border.
At the time, Eritrea denied it was planning for war.