Iran wants to ship some of the gas from the offshore South Pars complex, the largest in the world, east through the long-delayed pipeline to eastern markets.
Pakistan signed an agreement with Tehran in 2009 to secure 750 million cubic feet of natural gas per day through the pipeline.
Manouchehr Mottaki, the Iranian foreign minister, complained U.S. military activity was destabilizing the region, which he said "could create a new crisis" for Afghanistan and Pakistan, Pakistan's The News International reports.
He blamed Washington for trying to interfere with pipeline plans, meanwhile, by courting New Delhi.
"Growing relations between U.S. and India should not affect the relations of India with other countries of the region," he said.
Islamabad and Tehran are expected to sign off on formal agreements for the pipeline project in the coming weeks. Mottaki said there was no reason for hesitation despite the pressure from Washington.
"We must not allow any third country to interfere in the bilateral relations of Iran and Pakistan," he warned.