Damascus. At least 37 people have been killed after a suicide bomber blew up a truck laden with explosives at an army checkpoint in Syria’s central city of Hama, state media and opposition activists report.The man blew himself up inside the vehicle on Sunday on a busy road on the outskirts of the government-held city, the state news agency SANA said. It blamed the attack on "terrorists”, the term it uses to describe rebel forces trying to topple President Bashar al-Assad.The pro-opposition Syrian Observatory for Human Rights said the attack targeted an army checkpoint."At least 31 people, including regime troops, were killed when a man detonated a truck laden with explosives at a checkpoint near an agricultural vehicles company on the road linking Hama to Salamiyeh,” the Observatory said.The Britain-based group said the death toll was likely to rise, as "there are dozens of wounded, some of them in critical condition”.SANA said the explosion appeared to have set ablaze a petrol truck nearby, increasing the damage and casualties.Pictures on Syria TV showed firefighters trying to put out huge fires and black clouds of smoke rising from charred trucks and cars.Clashes were reportedly ongoing in the area and gunfire could be heard.On Saturday, activists said a suicide bomber from the self-proclaimed jihadist group Jabhat al-Nusra blew himself up at an army checkpoint in a Damascus suburb.More than 30 combatants from both sides were said to have been killed in the blast and ensuing clashes.In the first months after the uprising against Assad’s government erupted in March 2011, Hama saw some of the largest demonstrations against his rule.