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.

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

The monitors arrived in Homs following reports that 60 people had been killed in the past 24 hours in the province, according to reports by activists and Syrian television.

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.

Activists said that the heavy bombardment of the central city stopped Tuesday morning and tanks were seen pulling out of the streets. The Syrian Observatory for Human Rights said that at least 11 tanks withdrew from the perimeter of Syria's troubled district of Baba Amr in Homs on Tuesday.

Earlier Tuesday, activists reported that Syria security forces killed at least four people.

The 50 Arab League monitors now in the country, who include Iraqis, Tunisians and Algerians nationals, are supposed to ensure compliance, though so far there is no sign that Assad is implementing any of the terms.

Another 100 monitors are set to arrive by the end of December.