Security forces shot dead at least 19 people in Syria on Thursday, many of them in cities that an Arab League delegation will tour to check compliance with a plan to end a fierce crackdown on an anti-government uprising.

The Syrian Observatory for Human Rights said most of those were killed when Assad's forces opened fire on countrywide protests. Six died in the central city of Hama, where monitors recently arrived.

The group said security forces fired on a protest in Douma, a Damascus suburb, and killed four people. Enraged residents launched a civil disobedience campaign and thousands reportedly flooded the main square for a sit-in.

The activists have called for complete civil disobedience. The roads have been blocked, stores are shut down and the city is paralysed, said Rami Abdelrahman, head of the British-based Observatory.

Monitors did not announce plans to inspect Douma on Thursday but some residents said they saw cars with Arab League logos. If true, it would be the team's first surprise visit, but no residents have reported seeing or speaking to monitors.

(Reporting by Erika Solomon and Mariam Karouny; Editing by Louise Ireland)