A car bomb at a funeral procession on Tuesday in Damascus killed 12 people, Syrian state news agency SANA reported.
Some 48 people were injured in the blast, SANA said. It was the second such blast in the Jaramana area on Tuesday, after three people were injured when a bomb attached to a car went off, dpa reported.
The blast came as helicopters dropped leaflets on rebel-held areas near Damascus calling on fighters to lay down their arms or face "an imminent death," activist Haytham al-Abdallah told dpa.
One of the flyers read: "To all of you terrorists, drop your arms, or else you will die. We will cleanse Syria from your presence."
The Local Coordination Committees, a group of activists documenting violence, said that 82 people were killed across Syria. Most of them died in Damascus suburbs, where government forces carry out shelling attacks on a daily basis.
Activists said the neighbourhoods of Zamalka, Qaboon, Joubar and Ein Tarma were shelled.
State media said the operation of "cleansing terrorist remnants" continues, as troops have been carrying out a wide-scale offensive against areas on the outskirts of Damascus for the past five days.
Foreign Minister Walid al-Moallem accused the United States of supporting "terrorism in Syria" in order to curb Iran's influence in the Middle East. The US has allocated funds to help Syrian refugees and provide non-leather equipment to the rebels.
In Lebanon, shells fired from Syria exploded at a construction site in the al-Qaa border area, injuring three Syrian workers, Lebanese police said.
A bus carrying Syrians from the northern province of Aleppo flipped over onto its side when the driver lost control and hit a concrete barrier at the Masnaa border crossing, injuring at least 19 people, the Lebanese National News Agency reported.
The numbers of Syrians fleeing to neighbouring Turkey and Jordan are rising rapidly, according to new data issued by the United Nations High Commissioner for Refugees (UNHCR) on Tuesday in Geneva.
Up to 5,000 refugees have been arriving in Turkey each day over the past 14 days, compared to around 500 in the previous weeks, UNHCR spokeswoman Melissa Fleming said. In Jordan, the number of people arriving at the Zaatari camp has doubled. More than 10,000 were registered in the past week.
The UNHCR said it had counted a total of 214,000 Syrian refugees as of Sunday, nearly 12,000 more than it had reported on Friday.