Syrian troops bombarded besieged districts of Homs on Thursday, as clashes raged unabated in the west of the central city for the fifth day a row, the Syrian Observatory for Human Rights said.
Six rebels were among seven people killed by regime shelling and overnight firefights in the Jobar district, the Britain-based watchdog said.
The Syrian Revolution General Authority, a network of opposition activists on the ground, said regime troops used heavy artillery and clashed with the rebel Free Syrian Army (FSA) in an attempt to storm the west side of the city.
"The Syrian regime has escalated its attack on Homs city and its environs in order to disperse the people on sectarian lines and achieve what it believes will be a final victory over Homs," said the Syrian National Council (SNC), a major part of the opposition in exile.
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"The regime uses the most heinous criminal methods against human beings... shelling with heavy weaponry, blocking off areas to prevent the bare necessities -- food, medicine -- from entering, sending in sectarian militia to wreak havoc and kill, and finishing with massacres of entire neighbourhoods and villages."
The SNC called for a nationwide rescue campaign, for the "FSA all over Syria to aid their comrades in Homs with equipment and men" and for aid agencies to give priority to the trapped and displaced people of Homs.
Elsewhere on Thursday, air raids struck the embattled town of Daraya near Mazzeh military airbase southwest of the capital Damascus and the rebel-held town of Yabrud far to the northeast, the Observatory said.
It also reported fighting near Aqraba alongside the Damascus airport road.
Warplanes also raided Busra al-Harir in the southern province of Daraa and Kfar Zeita in the central province of Hama, as rebels clashed with troops near the Nayrab and Kweyris military airports in the northern province of Aleppo.
On Wednesday, 109 people were killed nationwide in Syria, including 42 in Aleppo province alone, according to Observatory which relies on a wide network of activists and medics to compile its tolls.