At least 20 people were killed Monday by Syrian security forces in the restive city of Homs, the Syrian Observatory for Human Rights said, a day before the Arab League observers were due to visit and inspect the area.
"The toll has risen to 20 martyrs documented by name and the circumstances of their deaths," the Syrian Observatory for Human Rights said. "Fourteen died in the continuous shelling on the Baba Amr neighbourhood and six were killed in random gunfire in nearby neighborhoods."
The violence came as around 50 Arab League monitors, headed by Sudanese General Mohammed al-Dabi, arrived in Syria to start inspecting areas gripped by violence, according to activists. The government has not yet confirmed their arrival.
A nine-member advance Arab team arrived in Damascus last week, to prepare for the monitors.
The arrival of the observers in Syria is part of a deal agreed to by President Bashar Assad's government with the Arab League last week.
It calls for the withdrawal of the Syrian army and militias as well as rebel forces, the release of detainees and an end to all forms of violence.
A total of 150 Arab monitors are due to arrive in Damascus by the end of the month.
On Sunday, the opposition Syrian National Council demanded that monitors go to Homs immediately to "fulfill their stated mission" saying Syrian forces were committing daily massacres.
Homs, in central Syria, has been a focal point of the government crackdown on anti-government demonstrations.
More than 5,000 people have been killed across the country since anti-government protests erupted in March, according to UN estimates.
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