Government air and artillery bombardments hit rebel-held areas of the Syrian city of Deraa, on the border with Jordan, on Tuesday after a two-day ceasefire expired, witnesses and the Syrian Observatory for Human Rights said.
A witness and two rebel fighters in Deraa said the army and its allies had resumed air and artillery bombardments in the city and the narrow strip of countryside separating it from the border.
At least six raids took place in Gharz in east Deraa and in the old quarter of the city, where the army resumed efforts to break rebel lines, the rebels said.
The witness said that barrel bombs, artillery shells and rockets were used in the bombardment. Clashes took place near a military base southwest of the city near the border with Jordan, the witness added.
If the army takes rebel-held parts of Deraa and the few kilometres between it and the border, it would split rebel areas of southeast Syria in half.
The Syrian military could not be reached for comment on the renewed action, which took place as US and Russian officials were holding talks on creating a "de-escalation zone" in southwestern Syria that would include Deraa.
US and Russian officials agreed a ceasefire, which ended on Monday, during talks in Amman aimed at strengthening goodwill before more detailed negotiations on setting up the "de-escalation zone", diplomats in Jordan said.
On Saturday the Syrian army said it would Suspend combat operations in Deraa for 48 hours in order to support "reconciliation efforts".
Rebels in the city and other residents have said this month that the army's bombardment of Deraa has intensified and claiming that the government brought more troops to the city.