* Explosion hits pipeline as troops, tanks deploy in city
* Sources say rebels have re-armed in recent months (Adds details)
AMMAN, March 5 (Reuters) - An explosion hit an oil pipeline near the town of Quraiya in Syria's eastern province of Deir al-Zor on Monday as Syrian troops began a military operation in the region, opposition activists said.
They said a bomb appeared to have been detonated near the pipeline, which runs to a refinery on the coast, and smoke could be seen five km (three miles) away.
"The explosion was big. It occurred two hours ago as armoured trucks and tank carriers spread in the region. They already stormed two villages - Boqros and Mouhassan - in what could be a prelude to a fullscale military assault," Sheikh Ismael, one of the activists, told Reuters.
Syrian army tanks deployed in the city of Deir al-Zor, 60 km southwest of Quraiya, on Saturday to support forces and militia loyal to President Bashar al-Assad who came under rebel attack after three pro-democracy demonstrators were killed, opposition activists said.
Deir al-Zor is an oil-producing province situated on the Euphrates river bordering Iraq, from where opposition sources say weapons are smuggled to rebels operating under the flag of the loosely organised Free Syrian Army.
The sources say rebels in Deir al-Zor have been arming and organising 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.
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.
Assad sent tanks into the city in August to put down large street protests demanding his removal. They have since stayed on the edge of the city. (Reporting by Khaled Yacoub Oweis and Suleiman al-Khalidi; Editing by Alistair Lyon)