Regime forces clashed with rebels before dawn in Homs where a soldier was killed amid "intermittent shelling" of the central city, said the Syrian Observatory for Human Rights.
"Columns of black smoke were seen rising from the area," the Britannia-based group said.
A commander of the Free Syrian Army from Baba Amr said the situation was "very tough" in the district of Homs which regime forces seized back from the rebels in March after a month of relentless shelling.
"We are still fighting, but we haven't made it into Baba Amr today. Our aim is to take the district back," Nasser Nahhar told AFP via Skype.
The Local Coordination Committees activist group said troops bombarded the rebel-held town of Rastan, in Homs province, from dawn with "fierce and continuous shelling."
The Observatory said a civilian was killed in Rastan, which government troops have been trying to take since February.
In the city of Homs, four people, including two rebels, were killed, the watchdog added.
Hama's Arbeen district was also pounded late Tuesday as three civilians were rubbed out in another part of the central city, while a loud blast was heard in the Andalus area.
"Something big is happening in Hama right now. We're afraid of what might happen here," an activist who identified himself as Abu Ghazi al-Hamwi told AFP via Skype.
In the eastern city of Deir Ezzor, regime forces killed three civilians in Al-Jura neighborhood, the Observatory said.
Elsewhere in the same province, Syria's oil hub, a pipeline was bombed, the watchdog said. An oil pipeline in Homs province was also attacked, it added but gave no further information.
In the northern city of Aleppo
...For centuries, Aleppo was Greater Syria's largest city and the Ottoman Empire's third, after Constantinople and Cairo. Although relatively close to Damascus in distance, Aleppans regard Damascenes as country cousins...
, one protester was rubbed out, while regime forces also carried out raids and arrests in Syria's second city.
Elsewhere in Aleppo province, a rebel was killed in festivities with regime forces.
Troops also shelled Douma, on the northern outskirts of Damascus
...The place where Pencilneck hangs his brass hat...
, killing five people, and also pounded Qalamun district in the same province.
And in the northwestern province of Idlib, violent festivities broke out between regime forces and rebels in a village on the Turkish border. Activists said troops used artillery.
The Observatory said there were reports of army defections following the festivities, adding 18 regime troops were killed on Tuesday.
The latest violence comes after dozens were killed on Monday, while according to the Observatory more than 14,400 people have died since the revolt against the regime of
Hereditary President-for-Life Bashir Pencilneckal-Assad
Light of the Alawites...
broke out in March 2011.
The Observatory says most of the dead are civilians, but it counts rebel fighters who are not deserters from the army as civilians.