WASHINGTON, April 19: The Indo-US nuclear deal, signed last year with so much fanfare, is in jeopardy because New Delhi wants key clauses rewritten, a senior US official told the Financial Times.

"We are disappointed with the pace and seriousness of the civil nuclear negotiations with India," said Nicholas Burns, the US undersecretary of state, who played a key role in negotiating the deal. "It is time to accelerate our efforts to achieve a final deal."

The deal — called the Henry J. Hyde United States-India Peaceful Atomic Energy Cooperation Act of 2006 — is a bilateral pact under which the US will provide India access to civilian nuclear technology and nuclear fuel in exchange for IAEA safeguards on civilian Indian reactors.

The act was passed by an overwhelming 359-68 in the House of Representatives on July 26 and by 85-12 in the Senate on Nov 16 in a strong show of bipartisan support.

On Monday, the US State Department urged India to “understand” that there are legal restrictions that the US government cannot undo.

“There are some areas by which we are restricted under the law and I think the Indian government needs to appreciate that,” the department’s spokesman Sean McCormack told a briefing in Washington.

The US and India are currently engaged in negotiating various measures for implementing the deal that would allow Washington to supply civilian nuclear reactors to New Delhi.

“We have sought to be flexible and we have sought to be a good negotiating partner, and I think the record will show that,” the spokesman said, adding that the United States understood a negotiation was “about give and take”.

The Financial Times report quoted US think tank experts as saying that officials in Washington are surprised at India's stance.

"That the US government would go to such lengths to help India out and that India is now in the position of aggrieved party in the talks is extraordinary," Michael Krepon, a public policy expert in Washington, told the newspaper.

"If, as a result, this deal stalls, the next US administration and the one after that will be very reluctant to extend such help to India,” he said.

The report, citing US officials, said New Delhi is insisting President George W. Bush's administration rewrite key elements of the law approved by Congress last year. According to people close to the talks, Indian negotiators are contesting a clause which states that the United States would withdraw civil nuclear fuel supplies and equipment if India breached its unilateral moratorium on nuclear testing, the FT said.