Ammar Qurabi, the head of the National Organsiation for Human Rights said 26 people were killed in the province of Idlib and 13 in Homs. Two people were also killed in the eastern town of Deir Ezzor, one in Daraya , a suburb of the capital, Damascus, one in the coastal city of Latakia and one in central Hama.
Among the dead were a 12-year-old boy and four others aged between 15 and 18.
Fridays have become a rallying point in the nine-week revolts with protesters initially emboldened by the revolutions in Tunisia and Egypt.
Following a meeting with the Israeli prime minister in Washington, US President Barack Obama described the situation in Syria as one of “acute concern” for both countries.
Obama said he had briefed the Israeli leader on the “significant steps” his administration was taking to try to pressure the Syrian regime to reform.
But Syria has remained defiant in the face of diplomatic pressure, accusing the US of meddling in its internal affairs and of incitement.
Last week, the US imposed sanctions directly on President Bashar al-Assad while the European Union also placed sanctions on several of Assad’s aides although not on the president himself.
Human rights organisations say the regime’s brutal crackdown on protestors has left at least 850 people dead and hundreds more injured.