At least 15 people were killed in a suicide bombing on Tuesday outside the main international bus station in Damascus, Syrian state television reported.
"The explosion, which was a terrorist attack in front of the bus station in Somariyeh, was carried out by a suicide attacker," the report said, adding that 30 were wounded, dpa reported.
The Syrian Observatory for Human Rights, an watchdog group based in Britain, said the dead included two children and six Syrian soldiers.
The Somariyeh bus station handles bus and taxi departures for Lebanon, the main overland route out of regime-held areas in the Syrian capital.
Meanwhile, in Geneva, the World Health Organization (WHO) said that polio cases have started appearing in additional areas of the country, as it confirmed two new cases in rural Damascus and Aleppo, in addition to the 15 cases previously confirmed in the eastern province of Deir al-Zour.
In response to the outbreak, mass vaccination campaigns for 22 million young children are under way in the Middle East.
"Given the current situation in [Syria], frequent population movements across the region and subnational immunity gaps in key areas, the risk of further spread of wild poliovirus across the region is considered to be high," WHO said.
The organization has linked the lack of vaccinations during the Syrian civil war to the outbreak of polio, which can lead to paralysis and affects mostly children.