An army assault on Homs in central Syria entered its 13th day on Thursday, as the Muslim fasting month of Ramadan brought no relief to people in rebel areas, activists said.

"There isn't a minute that goes by that we do not hear the sound of a rocket or a shell hit the besieged (rebel-held) neighbourhoods, especially Khaldiyeh and Bab Hud," said Homs-based activist Yazan.

Districts in central Homs, dubbed "the capital of the revolution" by activists, have been under army siege for more than a year.

Speaking to AFP via the Internet on the second fasting day, Yazan said that "even before Ramadan, we were down to one meal a day".

Throughout the blockade, rights groups have warned of critical humanitarian conditions in rebel areas of the city, which come under daily shelling and frequent aerial bombardment.

The United Nations has said that some 2,500 civilians are trapped in the besieged neighbourhoods, and activists say there is no way out.

"The situation now is especially difficult for families who were forced to flee their homes because of the intense shelling" that accompanied the latest assault, said Yazan.

For about six months, people living in the besieged neighbourhoods of Syria's third city have relied on firewood or diesel fuel for cooking.

"We eat rice and bulgur to break our fast in the evening, and thyme and olives before daybreak," said Yazan.

"This is our second Ramadan under siege."

During Ramadan, Muslims the world over gather with family over festive meals after sunset. In Homs, however, "there is no electricity, no generators and no water wells" any more, said Yazan.

Lebanon's Shiite Hezbollah movement is taking part in the regime's military assault on Homs, says the Syrian Observatory for Human Rights.

Despite the difficulties and "the military imbalance, we plan on resisting here", said Yazan.

The assault on Homs comes after the army and Hezbollah retook nearby Qusayr, after a year-long siege of the once rebel-held town.

Elsewhere on Thursday, rebels seized Al-Bajariya village in the northeastern province of Hasakeh, which is home to a majority Kurdish population, said the Observatory.

The village had been under pro-regime militia control for several months, said the Britain-based group.

And in Damascus, the army bombarded the northeastern district of Qaboon, the watchdog said.

Clashes also raged on in flashpoints in Damascus' southern belt, and warplanes bombarded rebel-held villages in the countryside near the capital.

The Observatory estimates that more than 100,000 people have been killed in Syria's raging war.

The conflict began with peaceful demonstrations calling for regime change but morphed into an insurgency after the regime unleashed a crackdown on dissent.