Pakistani President Asif Ali Zardari is to meet with Iranian President Mahmoud Ahmadinejad along the border for a groundbreaking ceremony for a pipeline planned from the South Pars natural gas field in the Persian Gulf.
The United States objects to the project because of its potential economic benefit for sanction-strapped Iran. The government has expressed its concern to Islamabad about Zardari's decision.
Pakistan is searching for ways to cope with long-standing energy shortages. Moazzam Khan, a spokesman for the Pakistani Foreign Office, was quoted by the Dawn newspaper as saying energy needs were a fundamental concern for the government.
"We know about their concerns but we expect and hope that all our friends, including the U.S., will show more understanding on this issue," he said.
Pakistan is to have elections in May. Khan discounted rumors that Zardari's move may be a parting swipe to Washington amid growing anti-American sentiment in Pakistan.
"We are very clear about this project," Khan said. "It is in our national interest to go ahead with it."
Washington favors a rival project planned from Turkmenistan, which has the support of the Asian Development Bank.