India says it has made progress in talks with the US in Delhi aimed at ironing out key differences over a proposed landmark nuclear deal.
The US says India must split its civilian and military nuclear facilities
US Undersecretary of State Nicholas Burns and Indian Foreign Secretary Shyam Saran met ahead of US President George W Bush's India visit next week.
However, a White House aide sounded a cautious note saying a deal may not be agreed during the president's trip.
Under the deal India would gain access to US civilian nuclear technology.
National Security Advisor Stephen Hadley said the US would use the Bush visit "as a forcing function" to secure an agreement.
"If we can, great. If not, we'll continue to work on it after the visit's over," he told reporters.
Critics of the accord, which has to be ratified by the US Congress, fear it could harm non-proliferation efforts.
Following the talks, India's foreign ministry said in a statement that the two sides had had "detailed and productive discussions".
"There was greater clarity on the issues under discussion. Progress has been made in the talks," it said.
India's Prime Minister Manmohan Singh said the visit by Mr Burns had been "fruitful", the Press Trust of India news agency reports.
Ahead of Friday's talks, Mr Burns said there was a possibility the deal would not be finalised before Mr Bush arrived in India on 1 March.
But, he added: "President Bush and Prime Minister Singh have really given a clear signal, they both want to have this agreement done."
In an interview with the Times of India newspaper published on Friday, Mr Bush repeated the US position that India must separate its civilian and military nuclear programmes.
"First things first is to go to India and hopefully reach an agreement on separation, and then bring that agreement back and start selling it to the Congress," Mr Bush told the newspaper.
"But we can't bring anything back until we've agreed to the agreement."
Mr Bush acknowledged that resolving past differences would be difficult for both sides, but said working together could be a "confidence-building measure".
India's desire to bar international inspectors from its "fast breeder" programme has worried Washington.
An aide to Indian Prime Minister Manmohan Singh has said there is no question of opening up the fast breeder programme.
India wants to rid itself of US sanctions imposed in 1998
Fast breeder reactors are particularly suited to producing plutonium for atomic weapons.
"Who said we are going to put the fast breeder reactors in the civilian side? We cannot and will not do so," scientific adviser CNR Rao was quoted as telling the Press Trust of India.
"We will accept only whatever is good for India ... The deal cannot be forced on us. The country's interest will be protected."
If ratified by the US Congress, the controversial deal would 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, has said 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.
"This debate... has been hijacked over here [in the US] by non-proliferation theologians and in India by those rallying under the banner of self-reliance," he said.