Ethiopia will rerun parliamentary elections in at least 20 of the 524 seats contested during fiercely disputed polls, the chairperson of the National Election Board said on Friday.

Kemal Bedri said a new vote will be held in August. He said investigators found evidence of irregularities at more than 100 polling stations in those constituencies, and the number of re-elections could go up as probes are carried out in 40 other constituencies.

At least 40 people were killed and thousands arrested in protests over claims of massive fraud by the ruling party of Prime Minister Meles Zenawi during the May 15 polls.

“We don’t have all the investigation details in, but at the moment, we will hold re-elections in around 20 constituencies,” Kemal said.

The election board also is awaiting details of investigations of 139 constituencies but has thrown out complaints in 75 other seats.

He blamed the delays in announcing final results on the investigation process, which he said was new to Ethiopia, where the two previous elections were marred by irregularities.

Opposition parties have dismissed the probe as a “complete failure”, accusing the board of bias in favour of the ruling party, a claim dismissed by the board and the government.

So far, 307 seats have been declared out of 524, with the remaining 23 seats for the 547 member Parliament to be contested in delayed elections in Ethiopia’s Somali region.

The ruling Ethiopian People’s Revolutionary Democratic Front has won 139 seats while the main opposition group, the Coalition for Unity and Democracy, has 93 seats. Another opposition group, the United Ethiopian Democratic Front, secured 42 seats.

Dessalegn Rahmato, head of the independent Ethiopian think tank, the Forum for Social Studies, said the delays are fuelling anxiety and uncertainty in the country.

“Many people feel insecure because we don’t know what the results will be and how the parties involved will react to it,” he said.

“Now we don’t know when the final results will be out, maybe sometime in September. We are not sure and this creates a lot of unease.”

The elections were seen as a key test of Meles’ commitment to greater democratic reform in the country he has ruled for 14 years.

Britain has already frozen 20-million pound in aid after the demonstrators were gunned down. Both the United States and the European Union have called on the government to respect human rights and urged an independent inquiry into the killings.

Kemal said further announcements of results would be made early next week, although the overall winner will still be unknown.