A top US official has held a meeting with an Indian minister aimed at settling the details of a proposed landmark deal on nuclear co-operation.
India has pledged to open civilian nuclear sites to inspection
Undersecretary of State Nicholas Burns met junior foreign minister Anand Sharma in the capital, Delhi.
Mr Burns is in India for three days of talks with Indian officials.
He has said he is hopeful of overcoming obstacles blocking the deal, but that "hard work" remains to be done.
Experts say that despite assurances from both sides about the deal, talks between them have been bogged down.
Ahead of the deal, the American ambassador to India said that there were still outstanding differences between both countries.
Under the agreement, India will gain access to civilian nuclear technology and fuel from the United States.
India says two elements of the deal imposed by the US Congress will breach its sovereignty.
They concern reprocessing nuclear fuel, and a ban on any further nuclear weapons testing by India.
The planned deal overturns three decades of American policy on banning nuclear co-operation with countries which - like India - have not signed the Nuclear Non-Proliferation treaty.
Correspondents say the deal would make it more difficult for the US to rein in what it believes are the nuclear weapons ambitions of countries such as Iran and North Korea.
Under the deal US civilian nuclear trade will be permitted with India in exchange for safeguards, including UN inspections of India's 14 civilian nuclear plants.
Eight military plants would be off-limits.