At least 20,000 protesters gathered in Syria's Homs on Tuesday as Arab League peace monitors started their tour of the protest hotbed city, activists said.

Arab monitors are visiting Homs to determine if Syria is implementing a peace plan seeking to end a crackdown on nine months of revolt against President Bashar al-Assad's rule.

The Syrian Observatory for Human Rights said the group was gathering in Khalidiya, one of the four parts of Homs where there has been heavy bloodshed as armed rebels fight security forces using tanks.

(Reporting by Mariam Karouny; Editing by Louise Ireland)