* Limited fire, no impact on gas or oil output -sources
* 1st time energy infrastructure hit in attack since 2006
* Took place in Eastern Province where minority Shi'ites live (Adds details, analyst quote)
By Rania El Gamal and Angus McDowall
DUBAI/RIYADH, Sept 2 (Reuters) - A small fire broke out on a gas pipeline in eastern Saudi Arabia on Tuesday after assailants shot at a police patrol, security and oil industry sources said, in an incident that may heighten concern about the vulnerability of Saudi energy infrastructure.
The pipeline has been repaired and there was no impact on oil or gas production in the world's top crude exporter, the sources said.
But the incident marks the first time the kingdom's physical energy infrastructure has been damaged in a violent attack since 2006, when Saudi security forces foiled an attack by al Qaeda militants on the giant Abqaiq processing plant.
The brief fire was started by a bullet hitting the pipeline after shots were fired at a police car patrolling the oil-rich Eastern Province early on Tuesday, said Interior Ministry spokesman Major General Mansour Turki. One policeman was wounded in the leg, he said.
The news had little immediate impact on oil prices but many are keeping a watchful eye on the Middle East region, which is becoming increasingly fractured along sectarian lines.
"Given the already heightened tensions in the region at the moment, including between Sunnis and Shi'ites, any incident that leads to damage to Saudi energy infrastructure is going to be of concern to oil markets," said Simon Wardell analyst at IHS Global Insight in London.
International benchmark Brent crude oil was down $1.08 at $101.71 a barrel earlier on Tuesday, pressured by worries about slowing demand growth in China and Europe, a strong U.S. dollar and ample supplies.
A resident in the eastern district of Qatif said the incident had taken place close to a checkpoint at the entrance to the village of Awamiya, but that it had caused no damage to homes or other property.
"It wasn't very big or loud, but people in Awamiya and the neighbouring village of Safwa heard it," he said.
Awamiya in Qatif district has been the location of Saudi Arabia's most persistent unrest, with protests by members of the Sunni kingdom's Shi'ite minority in 2011 continuing until last year, coupled with occasional shooting and fire-bomb attacks on police.
There have been no confirmed attempts by Shi'ite activists to target Saudi Arabia's energy facilities. State oil firm Saudi Aramco is a major employer of Shi'ites in both Qatif and the sect's other main population centre in Eastern Province, al-Ahsa.
However, there was speculation in 2012 that a cyber attack on Aramco, which forced the oil company to replace thousands of computers, had been planned by local Shi'ite activists. Officials later said the attack had been planned abroad.
Saudi Shi'ites complain they face systematic discrimination from the country's Sunni-ruled government. They account for 10 percent to 20 percent of the population and live mostly in Eastern Province, where the biggest oil and gas fields are located.
Shi'ites say their areas receive less investment and that they are restricted in matters of public worship and mosque-building. They say they are not appointed to important jobs in local government and are subjected to slurs by senior Sunni clerics.
The government says there is no discrimination.
Protests in 2011 calling for more rights for Shi'ites and democracy were quickly quashed by the authorities, but sporadic protests continued and more than 20 people were killed. (Additional reporting by Reem Shamseddine in Khobar and David Sheppard in London; Editing by Jane Baird and Keiron Henderson)