President George W Bush has indicated the US has dropped its staunch opposition to a proposed gas pipeline from Iran to India via Pakistan.
The US "beef" with Iran is nuclear arms, not gas, said Mr Bush
Mr Bush said on his visit to Pakistan he understood the need for natural gas in the region and that the US argument with Iran was over nuclear weapons.
The $6bn project for the 2,600km (1,625 mile) pipeline will bring Iran revenue, Pakistan transit fees and India energy.
The nations hope to start construction in 2007, with key talks due this month.
The US had previously stated it was "absolutely opposed" to the gas pipeline, even indicating Pakistan and India could face sanctions if the project got under way.
But in Islamabad, Mr Bush said: "Our beef with Iran is not the pipeline, our beef with Iran is... they want to develop a nuclear weapon and I believe a nuclear weapon in the hands of the Iranians will be very dangerous for all of us."
He said he had discussed the pipeline with Pakistani President Pervez Musharraf and understood "the need to get natural gas in the region, that's fine".
Mr Bush said his secretary of energy would visit Pakistan to discuss Islamabad's energy needs.
However, Mr Bush indicated there was no current likelihood for a civilian nuclear deal between the US and Pakistan similar to the one he has signed with India.
Mr Bush said: "We discussed the civilian nuclear programme and I explained to him that Pakistan and India are different countries with different needs and different histories."
The US-India deal gives Delhi access to US technology although it has not signed the Nuclear Non-proliferation Treaty.
Pakistan said it had asked for similar treatment but Foreign Minister Khursheed Kasuri accepted things "do not happen overnight".
Two years ago Pakistani scientist AQ Khan admitted leaking nuclear secrets to countries such as Iran, Libya and North Korea.