Regional forces in southeast Ethiopia killed more than 150 al Shabaab militiamen during fierce border clashes on Friday, the state news agency and a regional commander said, in the third round of fighting in nine days.

The attacks add to the already complex security landscape in Ethiopia, where the central government is trying to put down an insurgency and calm paramilitary groups in two different regions, while starting peace negotiations in a third.

"The terrorist group regrouped its scattered forces (last night) and tried to infiltrate into Ethiopia and carry out (an) attack in the area bordering Somalia with Ethiopia," Tesfaye Ayalew, an Ethiopian army general told the state news agency ENA.

Al Shabaab have long sought to establish a base in Ethiopia and have, in recent years, broadcast messages in Afaan Oromo, a language spoken in Ethiopia.

Al Shabaab confirmed the fighting, claiming they had killed 103 Ethiopian police and occupied the town of Aato earlier on Friday.

A commander with Ethiopia's Somali regional forces rejected that death toll, saying only 14 regional Ethiopian fighters were killed.

"It's still in our control, it's not a question," the commander told Reuters, referring to Aato.

A resident of Aato town who asked not to be identified said al Shabaab attacked the town with car bombs and mortar shells in the morning but later fled.

The commander said federal Ethiopian forces carried out several air strikes, hitting four al Shabaab vehicles near the villages of Garasley and Lagalaay on the Somali side of the border, killing an unknown number of militants.

An al Shabaab leader had been killed in a mortar attack, he added.

Al Shabaab controls large swathes of Somalia and has killed tens of thousands of people in bombings in its fight to overthrow the Western-backed central government there and impose its own interpretation of Islamic law.