Syrian forces killed at least 31 civilians on Tuesday, including 16 in shelling of neighbourhoods in Homs, monitors said, as regime forces massed around the flashpoint city.
The Syrian Observatory for Human Rights said three children and a woman were among 16 people who died in "intensive shelling" that targeted the Homs neighbourhood of Baba Amr.
The Khaldiyeh and Karm al-Zaytoun sectors were also blitzed, the Britain-based monitoring group said.
Activists have said that in the past few days the regime has been bolstering its forces outside Homs, apparently to storm the city in central Syria following 18 straight days of siege.
The Observatory said a military convoy of 56 vehicles, including tanks and personnel carriers, were seen on Tuesday travelling on the highway from Damascus, near the town of Qarah, 70 kilometres (38 miles) south of Homs.
It said heavy shelling for two hours early on Tuesday of Khaldiyeh and Karm al-Zaytoun later gave way to more sporadic attacks.
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Elsewhere in Homs province, five other civilians, including a child, were killed when security forces opened fire at the border town of Qusayr, the Observatory said.
A civilian was also killed in gunfire that targeted the town of Al-Atarib, in the northern province of Aleppo, the watchdog said.
Two more were killed as troops opened fire in the village of Tronba, in the northwest province of Idlib, it added.
And seven others were killed in intensive gunfire by security forces that stormed the village of Abdita, in Idlib's Jebel al-Zawiya, the Observatory said.
AFP was not able to verify the reported death toll nor the reports of shelling as foreign reporters are given only limited access within the country.
Rights groups say more than 6,000 people have been killed in the regime's crackdown on protests against President Bashar al-Assad's regime that first erupted in March last year.
The Red Cross said on Monday it was in talks with Syrian authorities and rebels on a Homs ceasefire so that it can deliver aid, amid calls for women and children to be allowed safe passage out of the city.