Syria's army and security forces killed at least 27 civilians in a three-day tank-backed attack on the border town of Tel Kelakh to subdue pro-democracy protesters, a rights lawyer told Al Jazeera.
"There are 27 confirmed names. An unknown number of bodies were taken to the main hospital in Tel Kelakh and not handed over to their families," Razan Zaitouna said on Wednesday.
Tel Kelakh is a few kilometres from Lebanon's northern border with Syria.
Syrians pouring over the Lebanon border in recent days have described horrific scenes of execution-style slayings and bodies in the streets in the western town, which has been reportedly encircled by security forces.
Mustafa Osso, head of the Kurdish Organization for the Defense of Human Rights and Public Freedoms in Syria, said there were reports of gunfire in Tel Kelakh on Tuesday, but it was not clear whether there were injuries.
Syria's official news agency said eight soldiers and policemen were killed Tuesday and five others were wounded while pursuing fugitives in Tel Kelakh and nearby areas. The report said security forces arrested several fugitives and confiscated a large amount of weapons.
Syrian protesters have called for a one-day nationwide general strike, urging students to skip school and workers to bring commerce to a halt in a new strategy of defiance against government crackdowns that appear to be becoming more brutal and bloody.
The strike, planned for Wednesday, marks a shift by opposition forces to strike at President Bashar Assad's regime from new angles: its economic underpinnings and ability to keep the country running during two months of widening battles.
A sweeping popular acceptance of the strike call would be an embarrassing blow to Assad and show support for the uprising in places, such as central Damascus, where significant protests have yet to take hold and security forces have choked off the few that have taken place.
"It will be a day of punishment for the regime from the free revolutionaries ... Massive protests, no schools, no universities, no stores or restaurants and even no taxis. Nothing," a statement posted on the main Facebook page of the Syrian Revolution 2011 said.
Yet schools, shops and transport were operating normally in Damascus and other cities on Wednesday as a nationwide general strike called by the opposition appeared to go largely unheeded.
"Who would dare go on strike and risk losing their business or be targeted by authorities?" one businessman in Damascus who requested anonymity said.
Two activists contacted by the AFP news agency on Wednesday said that although the strike call may not be followed, demonstrations were planned later in the afternoon in several regions in the north and elsewhere.
The strike call came as the United States and European Union planned new sanctions against the Syrian leadership.
Hillary Clinton, the US secretary of state, warned on Tuesday of more pressure on Syria if the crackdown against pro-democracy protests continues.
Clinton said that both the European Union and the United States - which have already slapped sanctions on a number of senior Syrian officials but not on president al-Assad - were planning more steps.
"We will be taking additional steps in the days ahead," Clinton said, saying she agreed with Catherine Ashton, the EU foreign policy chief, who told reporters that the time for Syria to make changes was now.
Meanwhile, watchdog groups and Syrians fleeing into neighboring Lebanon added to the accounts of violence.
A Syrian rights activist, Mustafa Osso, said government agents chased and beat students taking part in a protest against Assad's regime at a university in Aleppo, Syria's second-largest largest city.
Security officials in Lebanon said at least 170 people entered the country Tuesday, including a 2-year-old girl with a shrapnel wound in her chest.
A pro-democracy activist in the central city of Homs expressed support for the nationwide strike, calling it "the only way to hurt the regime without putting people's lives at risk".
Yet the activist, speaking by phone to The Associated Press news agency, doubted the response would be big.
"The majority of businessmen and merchants are either supportive of the regime or fear for the businesses. They have too much to lose," he said, speaking on condition of anonymity for fear of reprisals.
A "mass grave" with 24 bodies, and another containing seven bodies including a father and his four sons, were discovered in Deraa on Monday. Calls to Deraa on Tuesday seeking to verify the reports were unsuccessful.
International rights watchdog Amnesty International urged Syrian authorities to carry out a prompt, impartial investigation into reports of the graves.
"If true, these reports of multiple corpses buried in a makeshift grave show an appalling disregard for humanity," said Malcolm Smart, Amnesty International's Middle East and North Africa director.
A Syrian interior ministry official dismissed the reports about a mass grave in Deraa as "completely baseless".