Twenty-one people, including four children and six women, are reported to have died after a minibus exploded in the southern Syrian town of Noa.
Opposition activists told the Syrian Observatory for Human Rights monitoring group that the bus drove over a mine planted by forces loyal to President Bashar al-Assad.
There was no immediate comment from the government.
This morning's explosion happened in the rebel-held territory in the Deraa province.
There are also army troops in the nearby base of Tel al-Jumaa, which is besieged.
Mr Assad's forces are battling a civil war that grew out of protests against his family's four-decade grip on the country.
Violence has continued despite pleas from regional Arab and Muslim organisations for a ceasefire to mark the Muslim festival of Eid al Adha.
The British-based Observatory, which is opposed to the Assad regime, reported clashes in most provinces today.
It said war planes had been deployed to the eastern desert city of Deir al-Zor.
The group said at least 27 government soldiers had been killed during intense clashes in Deir al-Zor over the past two days, although rebels gave a figure more than double that amount.