Three car bombs exploded in Syria's capital, Damascus, on July 2, with reports saying at least 18 people were killed.
Syrian police chased three suspected car bombers that were attempting to enter the capital, state television said.
Security forces stopped and detonated two of the vehicles, but the third driver entered Tahrir square in central Damascus and detonated his vehicle after being surrounded.
State television said the "terrorists" had intended to target busy areas on the first day back to work after the Eid al-Fitr holiday, which follows Ramadan.
There was no immediate claim of responsibility.
Footage broadcast by state television from one of the blast sites showed what appeared to be human remains and badly damaged vehicles outside a mosque near the Old City in Damascus.
The Britain-based Syrian Observatory for Human Rights, an opposition-run monitoring group, also reported the three explosions.
Initial reports said at least eight people were killed, but the Observatory later reported a total of 18 people dead, including at least seven pro-regime security personnel and two civilians.
Reports quoting medical sources put the number of the injured between 12 and 33. There was no immediate official confirmation of the death toll or the number of the injured.
Pro-government forces have been fighting to drive rebels from Ain Terma, one of their last strongholds in the Damascus suburbs.
Damascus, the seat of power for President Bashar Assad, has avoided the large-scale battles that have devastated other major Syrian cities during the country's six-year civil war.
But the capital was hit by two separate suicide bomb attacks in March.
Twin blasts that left 74 dead in the capital's Old City on March 11 and were claimed by former Al-Qaeda affiliate Fateh al-Sham Front, known before as the Al-Nusra Front.
On March 15, bomb attacks on a courthouse and restaurant in Damascus killed 32 people. They were claimed by the Islamic State group.
Syria's conflict broke out with anti-government protests in 2011, but has since evolved into a multi-front war that has killed more than 320,000 people.
Based on reporting by Reuters, AP, AFP, dpa, and BBC