At least 10 workers were killed Thursday when Syrian security forces stormed a farm in the restive southern province of Daraa, according to opposition activists. They gave no reason for the attack, DPA reported.
Heavy gunfire was, meanwhile, inside a military airport near the capital Damascus, said the activists.
They expected an imminent clampdown in the central city of Homs, another flashpoint in anti-government protests that started in March. Army troops are heavily deployed in districts of Homs as 12 personnel carriers moved into the city.
At least 12 people were killed in swoops by security and military forces across Syria on Wednesday, according to the Local Coordination Committees, a network of opposition activists.
Omar Idlibi, a spokesman for the Local Coordination Committees, said that "demonstrations will grip all Syria on Thursday marking six months since the uprising erupted against the regime" of President Bashar al-Assad.
"Six months. More than ever determined to continue the March 15 uprising," activists wrote on Facebook page The Syrian Revolution 2011, a motor of the popular revolt.
More than 40 people were arrested in the Jabal al-Zawiya region of Idlib, according to Idlibi who livesin Lebanon.
Reports from Syria are hard to independently verify as Damascus has barred most foreign media and human rights organizations from the country since pro-democracy protests erupted in mid-March.
An estimated 2,600 people have been killed since protests started in Syria in mid-March, according to UN High Commissioner for Human Rights Navi Pillay.