Syrians across the country voted Sunday in a referendum on a proposed new constitution, according to state media, as Secretary of State Hillary Rodham Clinton called upon them to abandon President Bashar al-Assad.

“The longer you support the regime’s campaign of violence against your brothers and sisters, the more it will stain your honor,” Clinton said to reporters in Morocco. “If you refuse, however, to prop up the regime or take part in attacks . . . your countrymen and women will hail you as heroes.”

Voting stations opened at 7 a.m. for a poll on a constitution that would technically mean the end of the Baath party that has dominated political life in Syria for the last 40 years, but which critics contend would do little to lessen Assad’s grip on the country and could legally allow him to remain in power until 2028.

The Syrian Arab News Agency published photographs of people lining up to vote and reported that there were polling centers in every province. But one resident of the Khalidiya district in the embattled city of Homs, parts of which have been bombarded by heavy artillery by government forces for more than three weeks, said he had seen no polling centers there. His and other reports were impossible to verify as Syria restricts access for reporters.

The referendum is the latest in a series of reforms made by Assad’s government under pressure from a nearly year-long uprising demanding greater rights and freedoms for Syrians.

Opponents of Assad’s rule have dismissed the referendum as inconsequential, arguing that the proposed constitution gives the president broad power to decree laws, appoint the government and dissolve parliament and seems designed to maintain the status quo.

“It is a pathetically transparent attempt to steer away the attention of Syrians and the world from the bestiality of Bashar al-Assad and his cohorts,” said Yaser Tabbara, a member of the prominent opposition Syrian National Council. He added that constitutional reform meant little because the current constitution’s guarantees of rights were not honored by the government, whose military crackdown against protest has been widely condemned by Western and many Arab leaders.

Activists said that 17 civilians died in violence Sunday, most in Homs. The International Red Cross, which is negotiating with Syrian authorities to remove the wounded, including two Western journalists, out of the besieged Baba Amr area, told Reuters on Sunday that no agreement had been reached.