Syrian government forces have shelled the eastern suburbs of Damascus and clashed with armed rebels there, activists and residents say.
Residents reported hearing heavy gunfire from about 6:00am local time (03:00 GMT) on Monday. They said the capital was shaken by several loud blasts, possibly artillery fire, two hours later.
"Every one of them feels like an earthquake," a resident in the central district of Adawi told the Reuters news agency, in a telephone call punctuated by two loud explosions.
The Syrian Observatory for Human Rights, a UK-based anti-government rights group, said that government forces were targeting rural areas around the Zamalka and Ain Terma suburbs on the eastern fringes of Damascus, a rebel stronghold in recent months.
It said Monday's army offensive came after President Bashar al-Assad's forces suffered heavy losses in the area on Sunday, when several military checkpoints came under attack.
The group also reported an attack in Salqin, a town in Idlib province near the northern border with Turkey, which reportedly killed at least 12 people, including several children. Footage posted online by activists showed several mutilated bodies in a pickup truck, as a man shouts that his son was killed.
The Observatory says more than 30,000 people, including 7,000 soldiers and members of the security forces, have been killed in Syria since the start of the uprising against Assad in March last year.
The army repelled a July rebel offensive in Damascus, but Assad's opponents are still present in outlying areas of the capital. Rebels also launched co-ordinated attacks on the army last week in Aleppo, trying to break a two-month military stalemate in Syria's biggest city.
Al Jazeera is unable to independently verify reports of violence, as the Syrian government has placed strict restrictions on reporting.
Explosion in Kurdish east
On Sunday, violence broke out in the Kurdish city of Qamishli, where a suicide car bomb killed four people, the first such attack in a region which has largely kept out of the conflict.
State television said at least four people were killed in the Qamishli blast, while the SOHR said eight members of the security forces were killed, and that the attack targeted their headquarters in the city.
In-depth coverage of escalating violence across Syria
"A suicide terrorist using a car laden with explosives attacked the western district of Qamishli," state TV reported.
The Observatory claimed that "at least eight members of the security forces were killed, and 15 were injured", adding that the blast was followed by heavy gunfire.
Sunday's bombing was the first time since the outbreak of the anti-government revolt that Qamishli witnessed such a violent attack, SOHR director Rami Abdel Rahman said. He said the military pulled out of Kurdish regions in northeastern Syria, including Qamishli, several months ago, and the rebel Free Syrian Army (FSA) had no presence in the city, although some other fighters are based there.
The Qamishli blast came as intense fighting swept Syria's second city Aleppo after a night of heavy shelling that destroyed houses and killed at least three people, including two civilians, said the Observatory.
Aleppo has been gripped by fighting on an unprecedented scale since Thursday.