The United States cannot renegotiate a historic nuclear energy deal with India which has drawn strong criticism from politicians in New Delhi, the main U.S. negotiator said in remarks published on Friday.

The comments by U.S. Undersecretary of State Nicholas Burns come amid a growing chorus of demands from communist allies of Prime Minister Manmohan Singh's government to scrap the historic pact they say is unfair and imposes American supremacy.

We can't renegotiate it because the agreement is done, a statement from India's Outlook magazine quoted Burns as saying in an interview.

Neither government wishes it to be renegotiated because it is now complete.

The interview is published in the latest issue of the magazine, due to hit the stands on Saturday.

Burns said he did not want to respond to criticism from India's left parties as that would amount to getting involved in Indian politics, the statement said.

So I don't have any particular message for them except to say that in the 21st century we have seen the global balance of forces shifting, he said.

That it is in the common interest of India and the U.S. to be partners, certainly on the effort to bring peace and stability in south and east Asia.

Washington's refusal to consider renegotiating the agreement came as communist parties, whose support is crucial for the survival of Singh's coalition government, began a two-day meeting on Friday to decide their strategy on the deal.

The agreement aims to give India access to U.S. nuclear fuel and equipment for the first time in three decades despite New Delhi having tested nuclear weapons and not having signed the Non-Proliferation Treaty.

But critics, including India's Hindu nationalist opposition, say it will eventually hurt India's nuclear security because of tough U.S. laws on nuclear trade governing the pact.

Singh has strongly defended the deal, saying it is crucial for India's development and would not impact New Delhi's foreign or security policies. Last week, he refused to budge and dared the communists to withdraw support.

While tough words have since been exchanged between the two sides and triggered fears that the coalition could be destabilized, the top communist leader indicated on Friday a compromise may be possible.

The honeymoon may be over but the marriage can go on, Prakash Karat, general-secretary of the Communist Party of India (Marxist), the largest of the four left parties in parliament, told reporters ahead of the party meeting.

U.S. India