BEIRUT, Lebanon - Tens of thousands of defiant Syrian protesters thronged the streets of Homs on Tuesday, calling for the execution of President Bashar al-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 uprising.

The pullback was the first sign the regime was complying with the league's plan to end the nine-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 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 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 that his 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 that Syria complies with the league's plan, the army stopped the bombardment and pulled back some of its tanks.

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 least two people were killed.

About 60 monitors arrived in Syria on Monday night - the first foreign observers Syria has allowed in since March, when the uprising against Assad's authoritarian rule began. The league said a team of 12 visited Homs.

After agreeing to the league's pullback plan Dec. 19, the regime intensified its crackdown on dissent; government troops killed hundreds in the last week, and Syria was condemned internationally for flouting the spirit of the agreement.

On Monday alone, security forces killed at least 42 people, most of them in Homs. Activists said security forces killed at least 16 people Tuesday, including six in Homs.

One group put Tuesday's toll at 30, including 13 in Homs province. Different groups often give varying tolls. With foreign journalists and rights groups barred from the country, the counts are virtually impossible to verify.

Amateur videos show residents of Homs pleading with the visiting monitors for protection.

"We are unarmed people who are dying!" a resident shouts to an observer. Seconds later, shooting is heard from a distance as someone else screams, "We are being slaughtered here!"

Given the intensified crackdown over the last week, the opposition has viewed Syria's agreement to the Arab League plan as a farce. Some even accuse the 22-state league of complicity in the killings. Activists say the regime is trying to buy time and forestall more international condemnation and sanctions.

"The Syrian government will cooperate symbolically enough in order not to completely alienate the Arab League," said Bilal Saab, a Middle East expert at the Monterey Institute of International Studies in California. "But make no mistake about it, its survival strategy is to keep kicking the can down the road, until domestic and international circumstances change in its favor."

Opponents of Assad doubt the Arab League can budge the leader at the head of one of the Middle East's most repressive regimes. Syria's top opposition leader, Burhan Ghalioun, called Sunday for the league to bring the U.N. Security Council into the effort. The United Nations says more than 5,000 people have been killed since March in the political violence.

Shortly after the tanks pulled back and stopped shelling, the videos showed tens of thousands flooding into the streets of Homs and marching defiantly in a funeral. They carried the open casket overhead with the exposed face of an 80-year-old man with a white beard.

"Listen, Bashar: If you fire bullets, grenades, or shells at us, we will not be scared!" one person shouted to the crowd through loudspeakers. Many were waving Syria's independence flag, which predates the 1963 ascendancy of Assad's Baath party to power.

"The people want to execute Bashar," a group of people chanted as they walked side by side with monitors through one of Homs' streets.

Homs, Syria's third-largest city with 800,000 people, is at the epicenter of the revolt against Assad. It is about 100 miles north of the capital, Damascus. Many Syrians refer to it as the "Capital of the Revolution."