US Secretary of State Hillary Clinton said Syria cannot now return to the way it was before anti-regime protests erupted on March 15.
Rights activist Abdel Karim Rihawi said the deaths also included two in Kadam and four in Douma, both suburbs of the capital, in addition to three in the northwestern city of Idlib and two more in the southern town of Daraa.
Neighbourhoods in Damascus bore the brunt of the violence, with 12 killed in Qabun, three in Rukn Eddin and another in Barzeh, said Rihawi, who heads the Syrian League for the Defence of Human Rights.
The capital's suburbs also saw the death of a child killed in Jobar, four adults in Douma and one in Kadam. Three people were killed in the northern city of Idlib and two others in the southern town of Daraa, Rihawi added.
More than one million Syrians turned out in just two cities -- Hama and Deir Ezzor -- to protest against the regime of President Bashar al-Assad and demand the release of hundreds of detainees seized in earlier pro-democracy rallies.
"More than a million people demonstrated in Hama and Deir Ezzor," Abdel Rahman said. "It's a major development and a message to the authorities that protests are getting bigger."