Qiu Jiangang, vice president of the China National Nuclear Corp (CNNC), told a meeting in Beijing that the company was already looking beyond those deals to an even bigger plant.

"Both sides are in discussions over the CNNC exporting a one-gigawatt nuclear plant to Pakistan," he said.

Qiu confirmed the two countries have signed contracts to build the No. 3 and No. 4 reactors of about 300 megawatts each at Chashma.

He did not give details about who was involved in discussions for the bigger plant and how far the talks had progressed.

The proposed expansion of China's nuclear power ties with Pakistan is likely to magnify unease in Washington, Delhi and other capitals worried about Pakistan's role regional security and nuclear proliferation.

Pakistan is a long-standing partner of China, and has been suffering chronic power shortages.

Beijing is wary of Indian regional dominance and U.S. influence. In 2008 Washington signed a nuclear energy deal with India that China and other countries questioned but ultimately let through.

Critics of that U.S.-India deal say it prompted China to deepen its own nuclear power cooperation with Pakistan, which has been beset by political instability and militant attacks.

Rivals India and Pakistan both possess nuclear arsenals and refuse to join the Nuclear Non-Proliferation Treaty, which would oblige them to scrap those arsenals.

Critics say Pakistan's domestic instability and its past role spreading nuclear arms technology demand that China's nuclear plans there at least come under stricter international scrutiny.

SHOWCASE

China says safeguards in place at Chashma ensure its role is entirely peaceful. The complex is China's first nuclear energy plant project abroad, and CNNC recently cast it as a launching pad for expanding into the global market.

"We must rely on the Pakistan Chashma nuclear power project to improve our ability to contract for nuclear power projects abroad, and to open up the foreign market for nuclear energy," the company said in an essay recently published in Seeking Truth, a magazine issued by China's ruling Communist Party.

A senior Pakistani government official familiar with discussions between Pakistan and China on nuclear cooperation said, "We are facing acute energy shortages and these nuclear power plants are important for us to overcome these shortages."

"We as well as China have said time and again that all this cooperation is under the safeguards of the IAEA (International Atomic Energy Agency) and there should not be any worries or concerns about it," said the official, who demanded anonymity.

Chinese nuclear industry executives said at Monday's seminar that the expanding nuclear power sector abroad offered abundant opportunities.

China prides itself in building the Lingao reactor that began fully operating in the country's far southern Guangdong province last week in a record-breaking period of 57 months. (For a factbox in China's nuclear power plants and plans see)

"All these experiences have laid the foundation for the nuclear sector to go overseas," said He Yu, chairman of the Guangdong Nuclear Power Corp.

China plans a massive expansion of its nuclear power in the next decade, and has about 28 reactors currently under construction, some 40 percent of the world's total being built.

*Additional reporting by Chris Buckley in BEIJING and Zeeshan Haider in ISLAMABAD; Editing by Ken Wills and Sanjeev Miglani