At least five civilians were killed by Syrian government forces and militiamen, an opposition group said on Sunday as the Arab League stepped up pressure to halt the crackdown, DPA reported.
Damascus had not yet responded to a Sunday deadline from the Arab League to endorse a peace plan or face unprecedented sanctions.
Security forces at a checkpoint north of the town of Maaret al-Naaman, a hub for army deserters, shot dead a truck driver, said the opposition Syrian Observatory for Human Rights.
A pro-government militia force known as al-Shabeeha killed a man and his three children in the district of al-Waar in the province of Homs, a centre of dissent, the London-based monitors said.
The state news agency SANA reported security agencies had arrested dozens of suspects in Homs for allegedly smuggling gunmen, weapons and drugs into the country. The government has repeatedly blamed the unrest on "armed terrorist groups", allegedly financed by foreign powers.
A deadline set by an Arab League committee was to run out later Sunday. During talks in Qatar on Saturday, five Arab foreign ministers had asked Damascus to allow in Arab observers within 24 hours or face sweeping economic sanctions.
The ministers also approved a freezing of the assets of 19 top Syrian officials and banned them from travelling to Arab countries.
More than 4,000 people have been killed in Syria since mid-March, according to the latest United Nations estimates.