Under Secretary of State Nicholas Burns said he planned to visit New Delhi "in the next week or two" to try to conclude a deal that would cement a dramatic turnaround in US-Indian ties from their Cold War frostiness.

"We're 90 percent of the way there," Burns said at the Heritage Foundation, a conservative think-tank in Washington, after a long and convoluted series of meetings over the implementation of a pact first agreed in July 2005.

Indian critics fear it will hamper their country's nuclear weapons programme, nine years after the world's largest democracy staged atomic bomb tests that sparked a tit-for-tat response from arch-rival Pakistan.

Burns acknowledged that it had "taken longer than we thought to nail down ... the enormously complex" agreement, which now hinges on questions like India's willingness to admit UN inspectors to sensitive nuclear sites.

"Both sides need to compromise in order to reach a final agreement."

If sealed, the agreement would give energy-hungry India new access to nuclear power to sustain its stunning economic growth of recent years.