Eritrea and a faction of the Tigray Liberation Front are actively preparing for war against Ethiopia, the Ethiopian Foreign Ministry said, quoted by Agence France-Presse, BTA reported.
Relations between Addis Ababa and Asmara have been extremely tense for several months.
In a letter addressed to UN Secretary-General Antonio Guterres, the Ethiopian Foreign Ministry accused Eritrea and "an extremist faction of the Tigray Liberation Front" in financing, organizing and leading armed groups, mainly in Amhara state, where the Ethiopian army is fighting rebels.
"The cooperation between the Eritrean government and the Tigray Liberation Front has become apparent in recent months," says Addis Ababa, which says Eritrea is the main player who wants "Ethiopia to be destabilized and fragmented".
In recent years, relations between Ethiopia and Eritrea have deteriorated. Eritrea declared its independence from Ethiopia in 1993, after a long armed struggle. From 1998 to 2000, the two countries fought a bloody war over border disputes.