After years of delays and setbacks, not least bitter U.S. opposition, Pakistan is set to start work on its section of a $7.5 billion pipeline that will pump badly needed natural gas from Iran's Persian Gulf field.

But trouble's brewing in Pakistan's turbulent Balochistan province through which the 485-mile Pakistani part of the 1,200-mile pipeline will pass on its way to Pakistan's energy-short industrial north.

Balochistan, in southwestern Pakistan, long neglected by Islamabad governments, has seen sustained clashes between security forces and tribal separatists over the last decade.

It's also reportedly a base for Iranian Balochis who, with U.S. backing, have been waging an insurgency seeking autonomy from Tehran.

The United States and Saudi Arabia, reprising their double act in funding and arming Muslim guerrillas in Afghanistan to fight the invading Soviets in 1979-89, are aiding the Sunni nationalist rebels of the Jundullah movement in Iran's Sistan-Baluchistan province fight the Shiite-dominated regime in Tehran.

Balochistan, which has huge natural gas reserves, is the kind of place where the Americans could stir up a lot of trouble for the Pakistanis, and the pipeline, if they so chose.

It may already have started. The Islamabad government of President Asif Ali Zardari dismissed Balochistan's chief minister in January after several days of protests by minority Shiites incensed by an attack by militant Sunni rivals in which 96 people were killed in the regional capital, Quetta.

That put Balochistan under the direct control of Islamabad, which might prove useful if the pipeline triggers unrest in the province.

"The prime minister has allowed the deployment of all organs of the state, including the army, for the safety of Quetta," said Jan Ali Changezi, a member of the Balochistan provincial legislature.

The sectarian bloodshed, which extends across all of Pakistan, has nonetheless undermined Zardari's government.

Washington, which with Riyadh has pressured Islamabad for years to abandon the pipeline project because it will greatly benefit Iran, has threatened the Pakistanis with economic sanctions, like those imposed against Iran in 2010, if they go ahead with the pipeline.

But this time around, the Pakistani government, whose relations with the United States are severely strained over unilateral U.S. drone attacks on suspected al-Qaida hideouts, seems determined to defy Washington because the pipeline's vital for tackling mounting energy shortages.

Under the deal between the National Iranian Oil Co. and Pakistan's Interstate Gas System, Tehran will provide 750 million cubic feet of gas per day for 25 years from its giant offshore South Pars field in the Persian Gulf.

Iran, for whom the pipeline is a symbol of its defiance of the United States and its ever-tightening sanctions, has offered Islamabad a $500 million loan to help finance the project.

Pakistan's segment of the pipeline will cost about $1.5 billion. A senior Pakistani official said, "The Iranians have said they'll provide more funding if there's a need."

Zardari's chief adviser on energy affairs, Asim Hussein, says the pipeline from Iran is "a feasible project for Pakistan. It's the quickest route, the cheapest route where we can fulfill our energy needs."

He said Pakistan needs 8 billion cubic feet of gas per day but produces only 4.2 billion bcf and has no facilities to import liquefied natural gas.

Iran has almost completed its 570-mile leg of the pipeline to the Pakistani border.

The project was first mooted in 1994 and intended to carry gas from Iran through Pakistan to India, Pakistan's longtime Hindu-majority adversary. It was seen as a peace pipeline between the two, who have fought four wars since separation in 1948.

New Delhi, heavily pressured by Washington but citing price disputes, withdrew from the project in 2008.

Energy-hungry China has long expressed interest in the pipeline and has said it would seek to import 1 bcf a day if India pulled out.

Beijing's current position isn't clear but the Americans wouldn't be happy to see the Chinese moving in to boost their energy supplies.

The Chinese have built a deep-water port at Gwadar, on Pakistan's Indian Ocean coast that could be the southern terminal for a gas/oil pipelines into China.

They're also discussing with Pakistan a proposed trans-Himalayan pipeline to carry Middle Eastern crude to western China. Pakistan is the shortest possible route to import energy from the Persian Gulf.