US President George W Bush has urged India to separate its civilian and military nuclear programmes, ahead of his visit to Delhi next week.
There are fears the deal may boost India's nuclear arms programme
Speaking to the US-based Asia Society, Mr Bush said India needed to devise a "credible" plan to keep its US-aided civilian nuclear programme separate.
He said: "It will take time and it will take patience from both our countries."
India's desire to bar international inspectors from its "fast breeder" programme has worried Washington.
Mr Bush said the agreement would help "strengthen the bonds of trust".
"I'll continue to encourage India to produce a credible, transparent and defensible plan to separate its civilian and military nuclear programmes," he said.
India says it wants nuclear power to meet its energy needs
The controversial deal with the US, which has yet to be ratified by the US Congress, will give India access to nuclear fuel and technology, including reactors.
There are fears it could help India develop more powerful nuclear weapons. India is bordered by two other nuclear-armed states, Pakistan and China.
India is required to place its civilian nuclear facilities under international safeguards and open them to inspection by the International Atomic Energy Agency (IAEA).
India's Ambassador to Washington, Ronen Sen, told journalists that criticism that the agreement would augment India's nuclear arsenal did not "hold water".
He said India's nuclear weapons programme was indigenous and did not require outside assistance.
"We have not obtained them through covert means from third countries or with covert agreements with third countries," he said at Washington's National Press Club on Tuesday.
"This debate... has been hijacked over here [United States] by non-proliferation theologians and in India by those rallying under the banner of self-reliance," he said.