May 12, 2006 (Addis Ababa) —Nine bombs exploded across Ethiopia‘s capital Friday, killing four people and wounding dozens in what police said was a coordinated attempt to discredit the government.

The attacks came days before anniversary Monday of last year‘s general election. International observers had called the balloting seriously flawed and opposition politicians have refused to take up their posts to protest what they called government rigging.

In the past, other groups such as Oromo Liberation Front and the Ogaden National Liberation Front, both fighting for greater autonomy for their regions, have claimed responsibility for attacks outside Addis Ababa. Agents from neighboring Eritrea are also frequently blamed.

Demsash said a special investigative team would work day and night to track down those responsible. He declined to discuss suspects.

Four bombs exploded in the morning, followed by a lull before five went off after midday. The bombs struck across the city, but four exploded in the busy Mercato, the main shopping district.

The next blast damaged the headquarters of the city electricity company, injuring seven. Then an explosion blew out the front of a city bus, injuring seven, witnesses said.

"I was shocked," she said. "All of a sudden my son was on the ground bleeding."

Tiny holes dotted the walls where bomb fragments appeared to have hit, and the floor was covered with pools of blood.

A second afternoon blast destroyed a minibus taxi in front of a secondary school, witnesses said. There were no immediate reports of casualties.

It was not clear which attack had caused the fourth death.

The free press group Reporters Without Borders called Friday on the government to release political prisoners arrested following last year‘s election, including 21 journalists charged with treason and genocide. Most of the prisoners were arrested in November and December, when most of the country‘s independent newspapers were shut down.

The group called on Prime Minister Meles Zenawi to release the prisoners on Monday under an amnesty program designed to ease political tensions in the country.