WASHINGTON, March 11 (Xinhua) -- The United States on Monday threatened sanctions against Pakistan as the South Asian nation pressed ahead with a gas pipeline project with Iran.

"As I said, if this project actually goes forward, we have serious concerns that sanctions will be triggered," State Department spokeswoman Victoria Nuland told reporters at a regular news briefing.

"We've been straight up with the Pakistanis about these concerns," she said.

Despite Washington's strong opposition, Iran's President Mahmoud Ahmadinejad and his Pakistani counterpart Asif Ali Zardari inaugurated on Monday the 7.5-billion-U.S.-dollar project in Iran' s southeastern city of Chabahar, as Ahmadinejad said the West "has no right to obstruct" the project which will link Iran's gas pipeline to that of Pakistan.

Washington and its allies expanded their sanctions last year to target Iran's oil exports in their efforts to force the Islamic republic to stop its uranium enrichment activities, which are suspected of being used to make nuclear weapons.

"As we've talked about here before, what the legislation calls for is for our partner countries to be making a concerted effort to reduce their dependence on Iranian oil over time so we are able to waive sanctions as we see reductions being made," Nuland said.

She said Washington is supporting "large scale" energy projects in Pakistan that will add some 900 megawatts to the power grid by the end of 2024, fueling an additional 2 million households.