Syrian forces shot dead at least four demonstrators demanding foreign intervention to stop a crackdown on eight months of protests against President Bashar al-Assad and killed two other civilians in raids on their homes, activists said.

The killings occurred in the Damascus suburb of Douma, the central province of Homs, the southern province of Deraa on the border with Jordan and in the eastern province of Deir al-Zor near Iraq, the Syrian Observatory for Human Rights and other activist organisation said.

It was difficult to confirm the killings independently. Syrian authorities, who blame the unrest on terrorists, have barred most independent media.

The protests broke out after Friday prayers, the day that has seen the largest demonstrations in the anti-Assad protest movement. Thousands of people chanted the people want the execution of the president in the Bab al-Amro district of Homs, 140 kms (88 miles) north of Damascus, which has taken the brunt of tank bombardment on the city.

In the Bayada district of Homs men and women danced to songs exalting freedom at a rally led by Abdelbaset Sarout, a 21-year-old football star turned activist, live footage broadcast by activists showed.

We want Arab and international protection in any form, read a banner carried by members of the crowd.

Exiled dissident Rami Abdelrahman, president of the Observatory, said army and security presence was heavier than usual in many parts of the country to prevent protests, on the day a deadline set by the Arab League for Syria to sign a deal allowing monitors into the country expired.

Large protests took place in areas where security forces stayed away, such as parts of Homs, Hama countryside and the province of Idlib (near Turkey), Abdelrahman said.

Citing residents, Abdelrahman said that in his hometown, the coastal city of Banias, 200 worshipers leaving al-Qubayat mosque in south Banias were confronted by security police double their number to prevent the crowd from demonstrating.

(Reporting by Khaled Yacoub Oweis, Amman newsroom; Editing by Louise Ireland)