AMMAN (Reuters/AFP) - Syrian troops fought rebels trying to seize central Aleppo on Tuesday and quelled a jail mutiny on the outskirts of the northern city, killing 15 prisoners, opposition activists said.

After a week of battles between President Bashar al-Assad’s forces and his opponents in Damascus, fighting intensified in Aleppo, a more populous commercial city that long seemed immune to the 16-month-old upheaval convulsing Syria.

Rebels seeking to capture downtown Aleppo were combating Syrian troops and intelligence men at the gates of the Old City, a UN World Heritage site, residents and activists said.

The deaths in the prison mutiny were caused when Assad’s forces used machineguns and teargas on inmates overnight, activists in contact with surviving prisoners said. At least nine people were killed in army shelling of al-Herak, a town south of Deraa, the cradle of the revolt against more than four decades of Assad family rule, activists said.

In Damascus, explosions and gunfire rocked the central district of Barzeh after government forces stormed in overnight, opposition activists said. Tanks prowled the streets of Midan, a neighbourhood recaptured by the army from rebels on Friday. Several shells landed in the southern suburb of Hajar al-Aswad, where Assad’s forces have been trying to dislodge rebels. Elsewhere residents buried their dead or ventured back to check on homes they had fled to escape the fighting.

Outside Damascus and Aleppo, Assad’s forces have used artillery and helicopter gunships to keep rebel fighters off balance in the last few days, while avoiding ground incursions, rebel and opposition sources said, saying Deir al-Zor and al-Herak were among towns suffering such long-range bombardments.

Shelling in the southern Syrian town of Herak killed seven children on Tuesday, a human rights group said, taking the nationwide toll to 42 as helicopters strafed the country’s second city Aleppo.

“At least seven children were killed by regime forces shelling of the besieged town of Herak,” the Syrian Observatory for Human Rights said.

A video distributed by the Britain-based watchdog showed the bodies of dead children, including a young girl in a pink and white dress, lying on a blood-smeared floor, the faces of some of them covered in blood.The Observatory put the nationwide death toll for Tuesday at 42, including at least seven people killed when regime forces put down a prison mutiny in Aleppo, which followed a similar rebellion at the main prison in the central city of Homs.

Syria has named General Ali Mamluk as the new head of the national security office in a shakeup of the security services after a bombing killed top figures last week, a security source told AFP on Tuesday. “General Ali Mamluk, who was head of state security, is becoming the head of the bureau of national security, with the rank of minister, overseeing the entire security apparatus,” the source said.