Amid allegations of high-handedness, the government said security forces acted to restore order.
An Associated Press reporter saw 11 bodies in a room in Addis Ababa's main hospital, at least four with gunshot wounds to the head, and was told they were only some of the casualties from a third day of protests in the capital over election results.
Doctors at two other hospitals reported an additional 13 dead and hundreds of injured, many with gunshot wounds.
Bereket Simon, the information minister, who is also the ruling party spokesman, said he did not have an accurate toll from the shooting, but said the opposition Coalition for Unity and Democracy (CUD) was behind the protests.
"Today, some of their followers - and some who wanted to use this opportunity for looting - have gathered in some parts of Addis and disrupted the smooth functioning of life. So the government had to use the anti-riot police to resolve the situation," the minister said.
He also said seven buses were destroyed and civilian cars were attacked and businesses and banks were damaged.
The government has denied
using excessive force
The protests have erupted despite Prime Minister Meles Zenawi's move to ban demonstrations immediately after the 15 May legislative election. Meles's party won a majority of seats in the election, according to official results.
Opposition parties say there was widespread fraud and intimidation, charges the ruling party denies.
The head of the EU observer mission in Ethiopia said on Wednesday that some opposition politicians had been placed under house arrest.
"The mission has conveyed to the government its condemnation of the home arrests and other harassment and
threatening measures imposed on the opposition ... leaders
in the last days, severely curtailing their political activities," said Ana Gomes.
Aljazeera learned that the Ethiopian authorities put the head of the CUD and his deputy under house arrest.
But a CUD leader said the party was not behind the strike.
"Our sense is that the government is deliberately targeting us and fomenting violence to stop the electoral process and then blaming it on the opposition," said party vice-chairman Berhanu Nega.
"We have been saying all along that the public must be calm and patient and wait for the outcome of the investigations into the election."
State-run radio broadcast a warning in Amharic to Ethiopians not to stage additional protests.
"With effect from today, especially after the issuance of this statement, the police and security forces will take stern action against those shouting in groups, trying to cause destruction of government and people's property and piling stones on the roads and trying to disrupt peaceful and legal movement of the people," the warning said.
Wednesday's shooting began after the army's special forces troops arrived at the central business district where protesters were throwing stones.
One of the injured, who refused to give his name because of fear of retribution, said the army fired on fleeing people. He said he was caught up in the protests, not taking part in them.
The Addis Ababa city police also shot at protesters, said another person lying on a hospital trolley after emergency treatment.
"The police were running at the crowd, firing shots. I got shot in my leg," the 22-year-old day labourer, who identified himself by one name, Getu, said. "I was just trying to get home to avoid trouble."
Atenyesh Mamo, a 39-year-old mother of two, said she was shot in the waist after opening the door to her home to bring her seven-year-old son in as protests escalated.
"I don't know why they shot me as all I was doing was looking for my son," she said while waiting for an X-ray. "I am very angry and I don't know why the soldiers want to shoot us."
"The police were running at the crowd, firing shots. I got shot in my leg. I was just trying to get home to avoid trouble"
Dozens of people were wounded in Wednesday's melee with gunshots to the chest, legs, arms and back. Most of the victims were young men.
Nearly an hour after the shooting, ambulances and private vehicles continued to bring the wounded to the city's main Black Lion Hospital. Several hundred people gathered there, some wailing, crying and shouting.
Taxi drivers and shop owners in the Ethiopian capital had gone on strike on Wednesday, after earlier protests that mainly involved students.
The city government had threatened to revoke licences from taxi drivers if they did not remove opposition symbols and posters from their vehicles during the election campaign.
The strikes - organised by people who distributed handwritten notes and text messages transmitted by cell phones - occurred after two days of violent protests by university students in which one was killed, hundreds were arrested and dozens injured.
The elections were seen as a test of Meles's commitment to reform his sometimes authoritarian government.
Before questions surfaced about the count, EU observers had called the campaign and voting "the most genuinely competitive elections the country has experienced", despite some human rights violations.