A car bomb in central Damascus has killed at least 19 people and injured 53, Syrian state television has reported.
Monday's blast, which state-run media blamed on “terrorists”, went off near the Sabaa Bahrat Square, one of the capital's biggest roundabouts.
The Syrian Central Bank, a mosque and a school are located nearby.
A correspondent with the AFP news agency said the blast caused extensive damage and that intense gunfire could be heard shortly afterwards. The blast damaged the AFP Damascus office, blowing out the windows, but no staff were hurt.
Television images showed thick black smoke billowing from damaged cars and several bodies lying in the street.
Paramedics were seen carrying on a stretcher a young woman wearing a jeans skirt, her face bloodied, into an ambulance.Shaken teenage students holding their backpacks were seen walking away.
Al Jazeera's Rula Amin, reporting from Beirut, Lebanon, said rebels had been hiding in buildings near the scene of the attack.
"When the security forces arrived after the explosion, they started firing at them, and that's when the gun battles erupted," she said.
"It's a major attack because despite the heavy security measures that the government had put in place to prevent such attacks, the rebels were able to penetrate it. In the past few days, the government had been launching its own pre-emptive attacks against rebel strongholds, and against what they consider strategic points around the capital."
The explosion is the latest in a series of car bombs and suicide bombings to hit the Syrian capital.
On March 21, a huge explosion ripped through a Damascus mosque killing at least 49 people, including a key pro-regime Sunni cleric. And a month earlier, on February 21, at least 83 people were killed in a spate of bombings in the city.
In another development, UN Secretary General Ban Ki-moon said on Monday that a UN inspection team was in Cyprus and ready to deploy to Syria to probe the alleged use of chemical weapons in the conflict.
Rebels and the regime have traded blame for an alleged March 19 attack in the village of Khan al-Assal in northern Syria.
"The UN is now in the position to deploy in Syria - in less than 24 hours all logistical arrangements will be in place," Ban said in The Hague after President Bashar al-Assad called on the UN to probe allegations rebels had used chemical weapons.
"All we are waiting for is the go-ahead of the Syrian government to determine if any chemical weapons have been deployed," he added.
However, the country's foreign ministry said on Monday that it will not accept a chemical weapons team.
A ministry official, cited by state news agency SANA, said "Syria can not accept such manoeuvres on the part of the UN secretariat general, bearing in mind the negative role that it played in Iraq and which cleared the way to the American invasion" of that country in 2003.
The UN estimates that more than 70,000 people have been killed since the start of the conflict in March of 2011.
An internal rights group estimated that nearly 9,000 government troops have also been killed.