The Syrian military pounded the rebel-held central town of Qusayr, killing 13 people, in an apparent preparation for a ground assault, activists said.
"After two days of calm, planes bombed the town of Qusayr in the early hours of the morning," Syrian Observatory for Human Rights director Rami Abdel Rahman said.
"At least 13 people, including rebels, were killed in these raids and in artillery and mortar fire by the army.
"It seems that this is preparation for a major operation," he added.
The Syrian Revolution General Commission, a network of activists on the ground, also reported an intense bombardment of Qusayr, which the Syrian regime has been trying to recapture.
"A rain of shells on the city, at the same time as artillery fire and mortar fire from dawn. Homes were destroyed and burnt down," the group said.
The Qusayr district of Homs province has been the focus of fierce fighting between government forces and the rebels in recent weeks.
Regular troops have been bolstered by militiamen and by fighters of Lebanese militant group Hezbollah, a staunch Damascus ally.
The area is considered strategically important because it connects the capital to the Mediterranean coast.