Wednesday's violence in Ethiopia in which 22 people protesting about election results were killed, has been condemned by European Union observers.
Many of the dead and injured had gunshot wounds
EU mission head Ana Gomes expressed deep concern at "the dangerous situation Ethiopia was now facing".
There is a heavy police presence on the streets of the capital which are quiet as a transport strike continues.
Addis Ababa has seen three days of street protests over the ruling party's alleged massive election fraud.
Final results have not been announced three weeks after the parliamentary election as reports of the fraud are investigated.
The United States, United Kingdom and United Nations have urged restraint from the government and opposition.
Ms Gomes also criticised the house arrest of the main opposition leader and his deputy on Wednesday.
Hailu Shawul heads the Coalition for Unity and Democracy (CUD), which denies organising student protests in Addis Ababa at alleged election fraud.
State radio blamed Wednesday's violence on "gangsters" while a government minister blamed the CUD directly.
EU observers have voiced concern over irregular vote counting and biased reports by the state-owned media.
The BBC's Mohammed Adow reports that Wednesday's shooting began after army special forces arrived at the central business district, where protesters were throwing stones.
However, it is unclear whether the gunfire came from the heavily armed troops or the regular police, our correspondent says.
Journalists reported seeing at least four bodies with bullet wounds in the head in one hospital and the number of injured was put at about 100.
Information Minister Bereket Simon told Reuters news agency shortly before reports of Hailu Shawul's arrest that the CUD would "have to take responsibility".
He told the BBC the opposition was trying to overthrow a legitimate government in what he called a Ukrainian-style revolution.
Protests began on Monday when some 500 students were arrested
According to the minister, seven buses were destroyed and businesses and banks damaged by looters. He denied police had used excessive force to restore order.
Speaking for the EU, Ms Gomes said her mission condemned "harassment and threatening measures" with regard to CUD leaders.
She confirmed that Berhanu Nega, the CUD's deputy leader, had been warned not to leave his home.
Some of the wounded told journalists they had not been involved in the demonstrations.
"I was looking for my son, I opened the door and I was shot," Ateneyesh Mamo, a mother of two hit in the pelvis, told AFP news agency.
Wednesday's killings came after two days of student protests in which police beat back protesters with batons and rifle butts, as well as firing warning shots in the air, witnesses said.
The UK Foreign Office has warned citizens travelling in Ethiopia to be cautious and says that tension is spreading to other towns and cities.
According to provisional election results, the ruling Ethiopian People's Revolutionary Democratic Front and its allies have won 320 seats so far, giving it a majority in the 547-member parliament.
The opposition have, however, won almost 200 seats - a huge gain from the 12 they had in the previous parliament.