Arab League observers arrived Tuesday at Syria's third largest city, Homs, following reports that 60 people had been killed in the past 24 hours in the province, activists and Syrian television reported.
The delegation is headed by veteran Sudanese military intelligence officer General Mohammed Ahmed Mustafa al-Dabi, they said.
Syrian opposition activists said the army began withdrawing tanks from Homs earlier on Tuesday.
The government-run Syrian television Al Dunia reported that the delegation has arrived and was already in meetings with the governor of Homs.
Mohammed Saleh says the heavy bombardment of the central city stopped Tuesday morning and tanks were seen pulling out of the streets.
Another Homs-based activist says he saw armored vehicles leaving early Tuesday on a highway that leads to the city of Palmyra to the east. He asked that his name not be made public for fear of retribution.
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.
"Many tanks remain inside the neighborhood, the army is hiding them inside government buildings. They also hid one inside an event hall," Rami Abdelrahman of the Observatory told Reuters.
Earlier Tuesday, activists reported that Syria security forces killed at least four people.
The shelling, concentrated on the neighborhood of Baba Amr, lasted overnight. Quoting hospital sources, Omar Homsi, an activist based in the area, told dpa that 60 people had been killed there since Monday and 70 wounded.
Meanwhile, the first batch of Arab observers, who arrived in Syria on Monday, left Damascus and headed to the province of Homs, an Arab diplomat in Beirut told dpa.
"Let us hope they will be able to accomplish their mission," he added.
Syria has been gripped by an uprising calling for the ouster of President Bashar Assad since mid-March. According to United Nations estimates, the government crackdown on protesters has killed more than 5,000 people.
Homsi meanwhile blamed an explosion at an oil refinery in Tablisa, also in Homs, on the government, saying that Syrian army helicopters were seen over the area shortly before the blast took place.
"The Syrian authorities carried out the attack to defame the nature of the peaceful uprising that started in March against this brutal regime," Homsi said.
He added that in the early hours of the morning, Syrian security forces had also stormed areas in the neighborhood of Douma, in the capital Damascus, following anti-regime protests which took place overnight in support of the people of Homs.
Arab League plan which was agreed on by Assad last week requires the government to 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.
The 50 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.
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