Syria unrest: Damascus blast and clashes kill many
Renewed violence across Syria has left dozens dead, as Arab League observers continue their mission to oversee a peace plan for the country.
In the capital Damascus, state TV said up to 26 people died when a suicide bomber detonated explosives near a bus.
Opposition groups say the government staged Friday's blast to influence the Arab League mission.
Elsewhere in Syria, activists say 35 people have been killed by security forces during anti-government protests.
The Damascus blast happened at a busy junction in the Midan district. State TV showed the shattered blood-stained windows of what appeared to be a bus carrying policemen.
Authorities say most of those killed were civilians, but some security personnel were among the casualties.
Syria's interior ministry said it would "strike back with an iron fist" to what it called "terrorist escalation".
State news agency Sana released images of an Arab League observer being shown dead bodies lying on the floor of a hospital.
Most foreign correspondents have been barred from reporting within Syria, but Ian Black of the UK's Guardian newspaper visited the scene and told the BBC's Newshour that body parts were being shown "very energetically".
"Somebody held up a glove filled with blood and said 'this is Syrian blood'. There was a sense that the Syrian authorities wanted to show what had happened.
"What we didn't see were any other bodies of the people who are said to have been killed. We left with the sense of this is a horrific spectacle but that maybe some of the details weren't quite as one might have expected."
The explosion also damaged a police station, witnesses said.
Interior Minister Ibrahim al-Shaar said a suicide bomber had "detonated himself with the aim of killing the largest number of people".
One police officer told BBC Arabic he had seen a man carrying a black bag walk towards people leaving the bus before detonating the explosives.
But the Local Co-Ordination Committee (LCC) activist group quoted a doctor at the Mujtahed hospital as saying most of victims had injured suffered gunshot wounds, not explosives injuries.
He said security forces had been deployed heavily at the hospital and that staff were later prevented from helping people injured at demonstrations.
Some medical staff also refused to treat protesters on the ground that they were "traitors", he said.
Two weeks ago 44 people died in similar blasts also blamed on terrorists but which opposition groups accused the government of staging.
The main opposition group, the Syrian National Council (SNC), said the attacks "clearly bear the regime's fingerprints".
Col Riad al-Asaad, leader of the Free Syrian Army - the main armed group fighting the regime - reportedly denied involvement in Friday's attack.
The US condemned the attack, saying violence was not "the right answer to the problems in Syria".
Arab League monitors are in Syria on a month-long observer mission trying to ensure compliance with a peace plan. However, activists say the government crackdown has continued, with scores of people killed.
French Foreign Minister Alain Juppe said on Friday that the mission was "not at present able to do its job properly".
Opposition activists have urged Syrians to take to the streets in mass protests ahead of an Arab League meeting in Cairo on Sunday which will debate the initial findings of the observer mission.
Meanwhile, activists reported further violence on Friday. Anti-government protests have regularly followed traditional Friday prayers.
The LCC said nine protesters had been killed in Hama, 14 in the suburbs of Damascus, eight in Homs, three in Idlib and one in Deraa. The numbers cannot be verified.
Sana news agency also reported that an oil pipeline between Hama and Idlib in the north-west had been blown up by a "terrorist group".
The UN says more than 5,000 civilians have been killed since protests against President Bashar al-Assad began 10 months ago.