A bomb blast in central Damascus killed at least 13 people on Tuesday, state media said, as US President Barack Obama voiced concern over the Syrian regime's alleged use of chemical weapons in talks with his Russian counterpart.
The bomb attack in the Marjeh district of Damascus came a day after Syrian Prime Minister Wael al-Haqi survived a car bombing in an upscale neighbourhood of the capital.
"The number of casualties in the cowardly terrorist blast targeting the commercial and historic centre of Damascus in the Marjeh district rose to 13 martyrs and more than 70 injured," state television reported, citing the interior ministry.
The Syrian Observatory for Human Rights reported "14 dead, including nine civilians and five members of the security forces, in a car bomb attack near the old interior ministry headquarters."
Official channels broadcast footage showing smoke billowing over the site of the explosion, which blew out windows of cars, knocking off the bumpers of some and starting fires.
The windows of the interior ministry building were blown out and a commercial complex, Burj Dismshiq, was devastated. Uniformed and armed plainclothes security forces could be seen running near the scene, as residents fled.
"Internationally-financed and supported terrorism committed a terrible massacre against civilians," state television said.
Several mutilated bodies could be seen lying in the street, and at least one body wrapped in a white sheet was laid out alongside an ambulance.
Fire engines were at the scene with firefighters battling several blazes.
"What mistake have we committed? I was going to work. Look at the bodies. Is this the freedom they want?" a bystander said to state media.
On Monday, a car bomb targeted Haqi's convoy as it passed through the capital's Mazzeh neighbourhood, killing one of his bodyguards and five other people, according to the Observatory.
Halqi, appointed prime minister in August 2012 after his predecessor Riad Hijab defected to the opposition, is the latest in a growing list of regime officials to be targeted for assassination.
In July 2012, a suicide bomb attack killed Syria's defence minister and deputy defence minister and seriously wounded the interior minister.
Damascus has seen a wave of major bombings in recent weeks, including on April 9, when a massive blast in the centre of the city killed at least 15 people.
As bloodshed continued unabated in Syria on Tuesday, Obama raised the issue of chemical weapons in a telephone call with his Russian counterpart Vladimir Putin.
"President Obama and President Putin reviewed the situation in Syria, with President Obama underscoring concern over Syrian chemical weapons," a White House statement said.
Obama is under pressure because he warned last year that the use or movement of chemical weapons by President Bashar al-Assad's embattled forces would cross a US "red line."
Key political players in Washington are now saying his credibility is on the line, though the White House is seeking more detailed intelligence into exactly how and when such weapons may have been used.
Washington has been deeply frustrated that Russia has blocked tougher action in the UN Security Council, including sanctions, against its long-time ally Syria.
The Observatory said air raids on Tuesday killed 15 people on the outskirts of Mennegh airport, near the northern city of Aleppo, that rebels have been trying to capture for months.
Warplanes also bombed the Jubar area of Damascus, and areas of Homs, Raqa and Latakia provinces.
On Monday, at least 159 people were killed in violence across Syria, according to the Observatory.
Underlining the dangers of covering the conflict in Syria, Italian daily La Stampa said one of its journalists, Domenico Quirico, has not been heard from since April 9.
Media watchdog Reporters Without Borders says seven journalists are now missing in Syria, while 23 others have been killed.