AMMAN - Syrian army tanks deployed in the eastern city of Deir al-Zor on Saturday to support forces and militiamen loyal to President Bashar Assad who came under rebel attack after three pro-democracy demonstrators were killed, opposition activists said."Old Russian T-54 tanks and armored vehicles have taken positions at main roundabouts. Every half an hour or so you hear gunfire by the Free Syrian Army directed at roadblocks manned by security police and 'shabbiha' (pro-Assad militia)," Abu Abdel Rahman, one of the activists, told Reuters from Deir al-Zor.The city, 450 km northeast of Damascus, is situated on the Euphrates river in an oil producing province bordering Iraq, from where opposition sources say weapons are smuggled to rebels operating under the flag of the loosely organized Free Syrian Army.Opposition sources say Free Syrian Army rebels in Deir al-Zor have been arming and organizing in the last two months as Assad's main forces were focused on trying to put down the revolt on the central city of Homs and its surrounding countryside."There are now ten Free Syrian Army brigades operating in Deir al-Zor and more weapons flowing from Iraq, but the rebels' organization is still lacking and security forces retain control on the city in daytime. At night the ground belongs to the rebels," Abu Abdelrahman said.Controlling the Sunni city would poise another major challenge for Assad, a member of Syria's minority Alawite sect, an offshoot of Islam that has dominated Syria for the last five decades by taking control of the army and security apparatus and then forging alliances under Assad's father, the late President Hafez Assad, with Sunni merchants and tribes.Deir al-Zor, situated deep in Syria's tribal heartland, is far from central supply lines and its inhabitants have strong links with kinsmen in Iraq's Sunni heartland.Tanks stormed the city in August to put down large street protests demanding Assad's removal, and have since stayed on the edge of the city.Syrian forces killed three young men Deir al-Zor earlier on Saturday when they opened fire at a funeral for two people killed in a crackdown on expanding pro-democracy demonstrations in the region, opposition activists said."The funeral was in al-Ommal neighborhood for Amira al-Salem and Omar a-Juneidi, who were killed on Friday. The mourners began chanting against Assad when the 'amin' (security police) started shooting from a hilltop," said activist Abdallah Mahmoud.