Residents said that gunfire could be heard around Addis Ababa as police tried to disperse protesters in a fourth day of unrest that has spread beyond the capital.

Since Tuesday, more than 40 people have been killed in Ethiopia’s worst political violence. No new casualties were reported on Friday.

Friday's clashes broke out when a crowd of youths gathered close to the AU headquarters attacked passengers of a public transport bus.

"The demonstrators stopped the bus, jumped on it and tried to set it on fire with petrol," said a travel agent handling the tourists.

Witnesses said protesters were targeting public transport because they saw the state-subsidised service as a symbol of authority. There was no immediate word on casualties.

A renewed protest against the disputed May 15 elections soon turned into a full-scale riot starting on Tuesday.