The latest deaths came after UN chief Ban Ki-moon called for "coherent" global action over President Bashar al-Assad''s deadly response to dissent, as dissidents marked six months of anti-regime protests in Syria.
And Turkish Prime Minister Recep Tayyip Erdogan, in Libya on the final leg of an "Arab Spring" tour, lashed out at Assad, telling him the era of oppressive dictators is past.
Erdogan is expected in New York next week, and the White House said President Barack Obama would discuss with him the crisis in Syria and wider turmoil in the Middle East.
In the central city of Homs, two demonstrators were shot dead by security forces when several thousand people gathered to protest, activists said.
One person was shot dead by security forces in the Nahr Aisha quarter of Damascus, and two in Douma, also in the capital, said the Observatory.
And 10 people were killed in Hama city, nearby Hilfaya and villages in the northwest of the country, the Britain-based group told AFP in Nicosia.
The Observatory also reported the discovery of 15 bodies in various cities, saying most had been killed in the past 24 hours.
State television said one member of the security forces was killed and another four were wounded at Basr al-Harir in southern Daraa province during an attack by "armed groups.