Pakistan is facing an energy crisis due to a 33 percent decline in natural gas supplies compared with last year. The government last month said it would ration natural gas to cope with the deficit.
Washington opposes the Iranian pipeline because of potential economic benefits for Tehran. Ties between Washington and Pakistan are at lows because of fall outs from the military conflict in neighboring Afghanistan and the May raid that killed Osama bin Laden in Pakistan.
Victoria Nuland, a spokeswoman for the U.S. State Department, said Washington had concerns about the status of the Iranian pipeline.
"We've made absolutely clear over many months now our concern about this deal and we will continue to talk to Pakistan about it," she said.
Western adversaries of Iran are tightening economic sanctions on Tehran in response to growing concerns over its nuclear program.
The Pakistani Ministry of Petroleum and Natural Resources last week said it had a series of measures it could take to address the shortages, including moving forward with the Iranian option despite U.S. reservations.