ADDIS ABABA, Ethiopia — Ethiopian security forces held a number of opposition leaders under house arrest Thursday, a day after police and troops fired into crowds killing at least 22 people in the country’s worst bloodshed in four years.

Troops patrolled deserted streets and, for a second day, most shops were closed. The violence on Wednesday flared after weeks of opposition accusations that the ruling party had intimidated voters and rigged the polls to hold on to power in the strategic Horn of Africa nation.

Some opposition leaders were being kept at their homes, party sources and European Union observers told Reuters.

“The mission has conveyed to the government its condemnation of the house arrests and other harassment and threatening measures imposed on the opposition,” EU chief observer Ana Gomez said late on Wednesday.

Prime Minister Meles Zenawi’s Ethiopian People’s Revolutionary Democratic Front (EPRDF) has ruled since 1991, when his guerrilla army deposed former military ruler Haile Mariam Mengistu.

Ethiopian authorities blamed the main opposition Coalition for Unity and Democracy (CUD) for inciting crowds to loot shops, rob banks and attack police on Wednesday.

But the CUD said the clashes, after two days of student protests in which one person was killed and hundreds arrested, were spontaneous.

The protests erupted Monday despite Prime Minister Meles Zenawi’s move to ban demonstrations immediately after the May 15 legislative election.

Preliminary results from the election board showed the ruling party and its allies have enough seats to form the next government in the nation of 72 million people, the continent’s top coffee producer.

Opposition parties say there was widespread fraud and intimidation, charges the ruling party denies.

Official results are due on July 8.

The elections had been seen as a test of Meles’ commitment to reform his sometimes authoritarian regime, analysts said.

Before questions surfaced about the count, European Union observers had called the campaign and voting “the most genuinely competitive elections the country has experienced,” despite some human rights violations.

But opposition and ruling parties have alleged that gunmen intimidated voters, people were forced to vote for certain parties, ballot boxes were stuffed or disappeared, and the number of ballots in some constituencies exceeded the number of registered voters.

Wednesday’s killings were the worst in Addis Ababa since police and security guards killed 41 people during April 2001 riots that followed a wave of student protests.