"Whether in Somalia and in other parts of the Horn of Africa -- including within Ethiopia -- Qatar has been one of the most important supporters of terrorism and extremism in our sub-region," Ethiopia's government said in an email statement.

Qatar rejected Ethiopia's charges.

Ethiopia, a U.S. ally and the biggest military power in the Horn of Africa, said it had long observed Qatar's "hostile behaviour", and had raised the issue directly on various occasions.

"All diplomatic efforts have been deployed to try to persuade Qatar to change its destructive activities ... of which Ethiopia has unequivocal evidence," it said. "Apparently blinded by arrogance ... Qatar has remained deaf to all our efforts."

Oil-rich Qatar, which is also an American ally, hosting a large U.S. military base, dismissed the accusations as "frivolous and irresponsible."

Ethiopia's statement added that Qatar's hostile behaviour "included the output of its media outlets", a presumed reference to the Al Jazeera Arab satellite television network.

JAZEERA REPORTS

Jazeera has in recent days been broadcasting reports on the conflict in Ethiopia's Ogaden region that have criticised the role of government troops against local rebels.

Ethiopia urged Qatar to "speedily change the misguided policies which have led to this unfortunate situation."

The statement cited Qatari support for Ethiopia's arch-foe Eritrea and backing for groups in Somalia where Addis Ababa has thousands of troops fighting Islamist insurgents.

"Qatar has left no stone unturned to cause harm to Ethiopia's national security. All those who are prepared to foment instability in Ethiopia and undermine the country's security have been given support and encouragement by Qatar.

"This has gone beyond Qatar's strong ties with Eritrea. It has indeed provided direct and indirect assistance to terrorist organisations in Somalia and other areas."

In Doha, a Qatari official dismissed Ethiopia's charges, saying it had always done its utmost to combat terrorism.

"The Ethiopian charges do not deserve a reaction from us. They are frivolous and irresponsible," the official, who declined to be named, told Reuters.

"Qatar's foreign policy is clear. Qatar underlines the importance of peaceful settlement of all disputes between nations.

Ethiopia's support for Somalia's Western-backed interim government has been a major source of contention in the region, and brought calls for jihad from some radical groups.

Bilateral trade is a negligible $6 million annually, according to Ethiopian officials.