“China and Pakistan have maintained cooperation in recent years in the civilian use of nuclear energy,” Foreign Ministry spokesman Qin Gang told reporters when asked about the US reaction to the deal. “This cooperation is in line with our respective international obligations and totally for peaceful purposes, and has International Atomic Energy Agency safeguards and supervision.”

The state-run China National Nuclear Corporation has agreed to finance two civilian nuclear reactors in Pakistan’s Punjab province, despite fears abroad about the safety of atomic material in the Islamic nation. The deal comes after China in 2004 entered the Nuclear Suppliers Group (NSG), a group of nuclear energy states that forbids exports to nations lacking strict International Atomic Energy Agency safeguards.

US State Department spokesman P.J. Crowley told reporters on Tuesday that Washington had asked China for more details on the deal.

“We have asked China to clarify the details of its sale of additional nuclear reactors to Pakistan. This appears to extend beyond cooperation that was grandfathered when China was approved for membership in the NSG,” he said.

The Financial Times reported in April that Chinese companies will build at least two new 650-megawatt reactors at Chashma in Punjab province. “This appears to extend beyond cooperation that was grand-fathered when China was approved for membership in the Nuclear Suppliers Group (NSG),” Crowley added. “We believe that such cooperation would require a specific exemption approved by consensus of the Nuclear Suppliers Group.”

The United States was expected to oppose the China-Pakistan deal next week at a meeting of the Nuclear Suppliers Group.

The 46-nation group controls trade in “dual-use” nuclear fuel, materials and technology to ensure they are applied only to civilian nuclear energy programs and not diverted into clandestine nuclear weapons work.

The Washington Post reported that China had suggested that the sale was grandfathered from before it joined the NSG in 2004, because it was completing work on two earlier reactors for Pakistan at the time.