Defying a warning from Washington, Pakistan's Prime Minister promised to go ahead with a plan to import natural gas from Iran, even if the United States levies additional sanctions against the Middle East country.

Yousuf Raza Gilani's comments came two days after the US special envoy to Pakistan, Richard Holbrooke, cautioned Pakistan not to "overcommit" itself to the deal because it could run afoul of new sanctions against Iran being finalised by Congress.

The deal has been a constant source of tension between the two countries, with Pakistan arguing it is vital to its ability to cope with an energy crisis, and the US stressing it would undercut international pressure on Iran over its nuclear programme.

Gilani said Pakistan would reconsider the deal if it violated United Nations sanctions but the country was "not bound to follow" unilateral US measures. He said media reports that quoted him as saying Pakistan would heed Holbrooke's warning were incorrect.

The UN has levied four sets of sanctions against Iran for failing to suspend uranium enrichment, a process that can produce fuel for a nuclear weapon. The latest set of UN sanctions was approved earlier this month.

The US has also applied a number of unilateral sanctions against Iran and Congress is finalising a new set largely aimed at the country's petroleum industry.

Pakistan and Iran finalised the gas deal this month. Under the contract, Iran will export 21.5 million cu m of gas per day to Pakistan through a new pipeline beginning in 2014. The construction of the pipeline is estimated to cost about US$7 billion ($10 billion).

While US officials have expressed opposition to the deal, Washington acknowledges that Pakistan faces a severe energy crisis and has made aid to the energy sector one if its top development priorities.

US opposition to the gas deal has also been tempered by Washington's reliance on Pakistani co-operation to fight al Qaeda and Taleban militants staging attacks against Nato troops in Afghanistan.

- AP