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Associated Press
This image made from amateur video and released by Shaam News Network Tuesday, Dec. 27, 2011, purports to show men carrying an injured man in Homs, Syria, Monday, Dec. 26, 2011.

BEIRUT — Tens of thousands of defiant Syrian protesters thronged the streets of Homs Tuesday, calling for the execution of President Bashar Assad shortly after his army pulled its tanks back and allowed Arab League monitors in for the first time to the city at the heart of the anti-government uprising.

The pullback was the first sign the regime was complying with the League's plan to end the 9-month-old crackdown on mostly unarmed and peaceful protesters.

Yet amateur video released by activists showed forces firing on protesters even while the monitors were inside the city. One of the observers walked with an elderly man who pointed with his cane to a fresh pool of blood on the street that he said had been shed by his son, killed a day earlier.

The man, wearing a red-and-white checkered headdress, then called for the monitor to walk ahead to "see the blood of my second son" also killed in the onslaught.

"Where is justice? Where are the Arabs?" the old man shouted in pain.

Syrian tanks had been heavily shelling Homs for days, residents and activists said, killing dozens even after Assad signed on early last week to the Arab League plan, which demands the government remove its security forces and heavy weapons from city streets, start talks with opposition leaders and allow human rights workers and journalists into the country.

But a few hours before the arrival of the monitors, who began work Tuesday to ensure Syria complies with the League's plan, the army stopped the bombardment and pulled some of its tanks back.

The British-based activist group Syrian Observatory for Human Rights confirmed that government forces fired on protesters while the monitors were inside Homs and said at two people were killed from the fire.