Syrian army troops on Saturday shelled areas in the dissident central city of Homs, a day after at least 40 civilians were killed by security forces across the country, activists said, DPA reported.
Helicopters were seen hovering over Homs, which has been a focal point for anti-government protests since March, the Federation of the Coordination Committees of the Syrian Revolution, a group of grassroots activists, said.
Security forces had opened fire indiscriminately in the neighbourhood of al-Khalidaya, but there were no casualties reported as yet, it said.
A large explosion early Saturday rocked the district of Baba Amr in Homs, the group added, giving no details about its cause or casualties.
Footage posted on the internet showed what activists said were overnight demonstrations in the city demanding the ouster of President Bashar al-Assad.
Armoured vehicles are, meanwhile, laying siege to the restive village of Mohassan in Deir al-Zour in north-eastern Syria as security personnel hunted for wanted protesters, according to activists.
They said that the security forces had made mass arrests in the village.
Meanwhile, five shells fired by the Syrian army on Saturday hit a border area near the Turkish city of Antakya, reported the broadcaster al-Jazeera.
It quoted a witness as saying that one shell had fallen near a Turkish border guards post.
The continuing clampdown contradicts an announcement by the United Nations on Wednesday that al-Assad had told UN chief Ban Ki-moon all military and security operations against protesters had been stopped.
Mass protests dubbed "Signs of Victory" were held Friday in several areas of Syria, a day after world leaders called for al-Assad to step down.
At least 1,860 civilians and 422 security personnel have been killed since pro-democracy protests began in Syria in mid-March, the London-based Syrian Observatory for Human Rights said.
It is hard to verify these reports, as the Syrian authorities have barred most foreign media and international human rights from the country.