BEIRUT — Thousands of angry mourners poured into the Syrian city of Homs on Monday in a politically charged funeral procession memorializing at least 20 protesters said to have been shot and killed by security forces loyal to President Bashar Assad a day earlier.

The march, described by witnesses and shown in amateur video posted on the Internet, along with smaller protests reported in Damascus, Latakia and Baniyas, were the latest signs that the weeks-long series of protests against the Assad government are not likely to abate any time soon. The government’s response, meanwhile, indicated that the longtime ruler has no intention of backing down either.

One witness said security forces completely cut off Homs, closing roads in and out of the city as truckloads of plainclothes pro-government militiamen called shabiha arrived to face off against young men who had taken off their shirts to show they were unarmed.

“”The people are chanting for freedom and the overthrow of the regime — the regime that oppresses people,”” said another Homs witness, who also declined to give his name due to safety concerns. “”The people will not submit to this oppression.””

Demonstrations against the Assad government began after the arrest and alleged torture of a group of teen vandals in the southern city of Dara more than a month ago. The peaceful popular movement was inspired by revolutions and uprisings across the Arab world.

Witnesses and political activists described a massacre late Sunday in Homs. An activist told Reuters that security forces on trucks roamed streets and opened fire on peaceful protesters angered by the death in custody of a tribal leader and insulted by an Assad speech in which he offered minor reforms.

Although the number of deaths could not be confirmed, one Homs resident who participated in the funeral procession told the Los Angeles Times that about 20 people were killed in Homs and more from the surrounding villages. Al-Jazeera reported that 25 people had been killed in Homs as of Monday evening.

At least two people were also killed Sunday in the city of Latakia.

“”The army opened fire on us without shame, without any guilt,”” said Mohammed, the Homs resident, reached by telephone. “”There was one martyr and we were doing a peaceful protest for him, and they opened fire.””

Widespread anti-government protests erupted across the country Sunday in what were widely seen as a rejection Assad’s promise to remove decades-old emergency laws that stifle civil liberties and replace them with counterterrorism measures that give his powerful security forces similar powers.

Although Assad has promised some moderate reforms, his other actions have made activists and observers doubt his sincerity. The country has launched an unprecedented crackdown on journalists, loading them into cars and locking them up for days without access to their families or attorneys.

The Syrian government alleges that the uprising is the work of foreign conspirators. The Washington Post, citing documents obtained by WikiLeaks, reported Monday that the U.S. secretly spent millions on democracy-promotion efforts in Syria, including an exile satellite television station based in London.