BEIRUT - Rebels killed 28 Syrian army soldiers on Thursday in an attack on three checkpoints around the town of Saraqeb, which straddles the country's main north-south highway, an opposition-linked group said.The British-based Syrian Observatory for Human Rights said that opposition activists in Saraqeb, in the northern province of Idlib bordering Turkey, confirmed the attacks had been carried out by several rebel units.Rami Abdelrahman, head of the Observatory, said that five insurgents were also killed in the attacks, two of which were on the highway linking the capital of Damascus to Aleppo, Syria's most populous city. The third attack was at a checkpoint on the road linking Aleppo with Latakia, a port city where Assad's forces remain mostly in control."The rebels have either destroyed or taken six vehicles. They will not stay at the checkpoints for long as Syrian warplanes normally bomb positions after rebels move in," he told Reuters over the phone.Rebels have relied on ambushes and street fights to make gains in the 19-month-old uprising against President Bashar Assad. The Syrian air-force has stepped up aerial strikes on villages, towns and cities across the country in retaliation.The army has lost swathes of land in Idlib and Aleppo province but is fighting to control towns along supply routes to Aleppo city, where its forces are fighting in many districts.