A Syrian protester in Amman, Jordan holds the national flag during a vigil calling for President Bashar al-Assad to step down. (Nader Daoud/AP)

CAIRO — Violent protests continued to roil Syria on Sunday as human rights activists reported that President Bashar al-Assad was using soldiers and tanks for the first time against demonstrators and sealing off the port city of Baniyas.

A day after the Interior Ministry warned that the regime’s leaders were losing patience with the nearly month-long revolt, four people were killed in the seaport north of Tartous as security forces and rooftop snipers opened fire on hundreds of demonstrators outside the Al-Rahman mosque, according to human rights workers who have been in touch with residents. Others reported that the military had ringed the city.

“I spoke to someone telling me he saw tanks going to the city,” said Nadim Houry, a senior researcher with Human Rights Watch’s Middle East and North Africa division.

SANA, the state-run news agency, reported Sunday that a soldier was killed in an “ambush” that afternoon while traveling the highway between Latakia and Baniyas. The agency said an “armed group” attacked from east of the highway.

It has been difficult to obtain independent confirmation of events in Syria. The government has made it difficult for news organizations to enter the country. And late Sunday, electricity was cut off in Baniyas after earlier outages of Internet and mobile telephone service.

Razon Zaitonah, a human rights lawyer who is in hiding in Damascus, said the appearance of tanks and military could suggest that Assad’s regime is willing to take even more extreme measures to put down the revolt.

Pockets of anti-government rebellion have spread across the country since about a dozen young people were arrested last month for anti-government graffiti in the impoverished southern city of Daraa. At least 37 demonstrators have been killed in protests after Friday’s midday prayers and the funeral services that followed.

SANA also said that funeral services were held Sunday for four members of the police and security services who had been killed in violent clashes Friday. The agency previously reported that 19 officers had been killed.

Syrian leaders continued to blame the revolt on “infiltrators” and a “U.S.-Israeli plot” to destabilize the nation, according to SANA.

SANA’s Web site also carried a report suggesting that work was underway to rewrite the hated 49-year-old emergency decree, perhaps to replace it with a new terrorism law.

Estimates of the number of demonstrators killed since the insurrection began March 16 have varied from 130, according to Human Rights Watch, to about 200, according to the Syria National Organization for Human Rights.