Eritrea on Monday rejected accusations by Ethiopia that it was responsible for military aggression and was backing armed groups inside Ethiopian territory as "false and fabricated", calling the claims part of a hostile campaign by Addis Ababa.

Ethiopia's foreign minister had accused neighbouring Eritrea over the weekend of military aggression and of supporting armed groups inside Ethiopian territory, where recent clashes between Tigrayan forces and Ethiopian troops have raised fears of a return to war.

"The patently false and fabricated accusations against Eritrea issued by Ethiopia’s Foreign Minister yesterday is astounding in its tone and substance, underlying motivation, and overarching objective," the ministry of information said in a statement.

"Sadly, it constitutes yet another deplorable act in a pattern and spiral of hostile campaigns against Eritrea for more than two years now," the ministry said, adding that it did not want to exacerbate the situation.

The two longstanding foes waged war against each other between 1998 and 2000, signing a peace deal in 2018.

They were allies during Ethiopia's two-year war against regional authorities in the northern Tigray region, but relations between the two nations have plunged into acrimony since then.

The February 7 letter from Ethiopia's Foreign Minister Gedion Timothewos to his Eritrean counterpart, Osman Saleh, said Eritrean forces had occupied Ethiopian territory along parts of their shared border for an extended period and had provided material support to militant groups operating inside Ethiopia.

Eritrea has bristled at repeated public declarations by Prime Minister Abiy Ahmed that landlocked Ethiopia has a right to sea access - comments many in Eritrea, which lies on the Red Sea, view as an implicit threat of military action.