Four people have been killed in an unprecedented clash between Syrian police and a team of bombers in the Syrian capital Damascus.
The blast apparently damaged only one, disused building
Police chased attackers armed with grenades after they set off a car bomb in an embassy district, officials said.
The state news agency said a policeman and a woman passer-by died along with two bombers. Two others were wounded.
The BBC's Kim Ghattas says officials are implying Islamic militants were responsible for the incident.
A disused building formerly used by the UN was burnt out by the blast.
Syrian TV has shown video of weapons including rocket-propelled grenades it said were from a cache used by the bombers.
Calm returned to the tightly policed city a few hours after the clash.
Our correspondent reports from Damascus that the violence is almost unheard-of in Syria where the authorities tightly control any dissent.
'Guns and grenades'
The blast took place on a main road leading into central Damascus from the Lebanese capital Beirut and happened near to the Iranian, Canadian and UK embassies in the city's upmarket Mazze district.
"There were at least a dozen blasts and several rounds of gunfire," witness Ted Guhl told BBC News Online in an email from the city.
Another witness, James Gordon, said it sounded like "hand grenades and light weapons".
Syrian media reported security forces had clashed with "terrorists" who had opened fire indiscriminately after planting a bomb "under a parked car".
"A clash ensued between the security forces and the terrorist group, which fled aboard a second car throwing grenades at the security forces," an interior ministry official told the state news agency.
Canadian and British officials said their embassies were undamaged and they were unaware of any casualties among their citizens.
The Syrian state news agency said the situation in Damascus was "fully under control".
Our correspondent says it is unclear who the bombers were or what their aim was and the authorities are only describing them as " terrorists".
Islamic unrest has not been reported in the country since the early 1980s when the security forces suppressed the Muslim Brotherhood organisation.
Syria, which is ruled by the Baath Party, saw violent incidents involving its Kurdish minority in March.
Earlier this month Jordan foiled an attack against its intelligence headquarters by suspected al-Qaeda militants which it said had infiltrated into the country from Syria.
Are you in the Damascus area? Did you witness the blasts?
They have now opened the Mazze Road and we just drove past the place. One building is heavily damaged, with its road side windows blown and blackened. No damage was seen on Canadian Embassy, although it is pretty close to the building. Also there were two large explosions already in the morning in the same are, however we are unsure whether these are related, but another road is still closed there.
Marko Lamminen, Damascus, Syria
I was on the mountain in the north of the city tonight while the incident was taking place. I am an American teaching at the Damascus Community School. There were at least a dozen blasts and several rounds of gun fire. We could hear the explosions which began around 7pm and continued sporadically for at least 15 minutes. We could also see smoke rising from the Mazze area. Tonight, armed soldiers rang the doorbell of apartments in my building in the Shalon area of the city (5 blocks from the American Embassy) and asked if I had a car outside on the street.
Ted Guhl, Damascus, Syria
I teach at a private university in Mazze Damascus, I had to flee with 70 students into an adjacent cactus forest, where we witnessed the live shooting and at least three terrorists were killed in front of our eyes. The Syrians were really tough, security measures were harshly and immediately imposed. The Iranian, Canadian, British and others are all intact. The UN headquarters are also just fine. There were only hand grenades and light weapons.
James Gordon, Syria Damascus
At about 19.30, I didn't look really on my watch, I heard an explosion and some gunfire. I couldn't see something, because there are some high buildings between me and the place where it took place. I live in the west of the city and it was for sure in the area that you described. I tried to phone some friends, but the Mobile-Net is out of function since the explosions happened. You can only phone by the regular line.
The Mazze highway also has the houses of many prominent members of the Baath party and the headquarters of the Baath party in Syria. Where the attack is described as being is not the UN compound, which is further out. There are a few Western style cafes and bars around the Mazze highway as well next to the Iranian and Canadian Embassies. It dos not, however, appear very clear at all what the exact target of the attack has been. SAR (the local news agency) is not shedding much light on the incident.
Duncan Burrell, Syria