Gunmen in south-western Ethiopia killed four police officers and prison warders, government officials say.
The killings took place during an overnight raid on a prison in Gambella, 450km from Addis Ababa.
The attacks were blamed on rebels from the semi-nomadic minority Anuak community who have been fighting against the security forces.
Diplomats in Addis Ababa told the AFP news agency they believed the death toll had been much higher.
They said gunmen had attacked a Catholic church before moving to the police station and then a prison, where they freed an unknown number of prisoners, possibly including jailed rebel fighters.
"Anti-peace forces attacked a police station in Gambella town and killed four members of the police, including the state police commissioner, and wounded six others," Gambella state security chief Senday Gach told the official Ethiopian News Agency.
He said that six of the attackers had also been killed.
Thousands of people have fled Gambella since the December 2003 massacre
"Members of the defence forces and the federal police are in hot pursuit of the culprits," he said.
"The culprits are those forces who incited the last conflict in the state."
Gambella, a lowland region whose indigenous population is ethnically distinct from the rest of the country, has been a scene of conflict for several years.
Earlier this year Human Rights Watch said the Ethiopian army had been killing, raping and torturing civilians in Gambella since the beginning of 2003.