The raids on the town of Ariha came amid intense clashes between government forces and insurgents in the northwestern province of Idlib and the central region of Hama.
The town, once a government stronghold, was captured by opposition fighters and Islamic militants in May. Government forces have suffered setbacks in Idlib province since March, including the loss of the provincial capital of the same name.
An activist group known as the Local Coordination Committees said the warplane crashed in a busy market, adding that it was not immediately clear whether it was shot down. The LCC said 27 people were killed and many others were wounded.
The Ariha Today Facebook page posted a photo showing at least seven buildings reduced to rubble on a narrow street. It said 27 people were killed but that 12 of them have not been identified yet. The group also listed 55 wounded, including nine women.
The Observatory and the LCC said that at the time of the crash, the town was under attack by Syrian President Bashar Assad's air force.