WASHINGTON (Reuters) -- The United States is close to reaching a nuclear cooperation deal with India and may clinch it before President George W. Bush visits there in March, a senior U.S. official said on Friday.

Bush and Indian Prime Minister Manmohan Singh agreed last July on an accord on civil nuclear energy that would reverse a nearly 30-year-old ban on atomic cooperation with New Delhi, which has tested nuclear weapons.

However details of that accord still have to be negotiated, including a plan to separate India's civil and military nuclear facilities. The deal also has to be accepted by the 44-nation Nuclear Suppliers Group and the U.S. Congress.

U.S. Undersecretary of State Nicholas Burns, who visited India last week to negotiate details of the agreement, told reporters he was confident a deal would be reached soon. "I think we have made a lot of progress over the last six months. I was not discouraged by my talks in Delhi last week," Burns told reporters. "That (a deal) might happen before the president's visit." Pressed further, he said: "It is my assessment, and I have been the one negotiating this for six months, that we are very close to an agreement."

In an interview with Reuters on Thursday, U.S. Secretary of State Condoleezza Rice said the two sides were making progress but India had to make some "difficult choices" for the final agreement to be reached. She declined to give specifics. Burns also said there needed to more progress on a few issues, which remained confidential. "I don't believe they are insuperable."