As Pakistani president arrived in Iran to sign Pak-Iran gas pipeline project, the United States warned Islamabad over any ‘sanctionable activity’, assuring assistance for energy needs.

"We recognise that Pakistan has significant energy requirements but we really think there are other long-term solutions to Pakistan's energy needs," said deputy acting spokesman Patrick Ventrell.

"And so we've been assisting as a government to contribute to the alleviation of the energy crisis in Pakistan," he said.

"It's in their best interests to avoid any sanctionable activity, and we think that we provide and are providing ... a better way to meet their energy needs in some of the assistance we're providing."

Iran's supreme leader Ayatollah Ali Khamenei has urged the visiting President Asif Ali Zardari to press ahead with a much-delayed $7.5 billion gas pipeline project despite US opposition.

Zardari arrived in Tehran on a 2-day official visit to Islamic Republic of Iran. The president will hold talks with Iranian leadership on a host of bilateral issues and the regional situation.