"There is no question that we've made some progress over the last six months but that much further progress has to be made and that there are some difficulties ahead of us," US Undersecretary of State Nicholas Burns said.

The official, however, said that he was keen to have an agreement in place before US President George W. Bush's visit to New Delhi in March.

"Our goal is to have an agreement before President Bush arrives," the official told reporters after two days of talks in New Delhi, where he discussed the deal with Indian foreign secretary Shyam Saran.

The talks followed an agreement signed between the two countries last July during a visit by Prime Minister Manmohan Singh to Washington.

Under the terms of the accord, India must separate civilian and military nuclear programs in exchange for advanced civilian nuclear technology. It would place its civilian nuclear reactors under International Atomic Energy Agency inspection.

Washington would ask the US Congress to amend laws to allow India access to technology normally reserved for nations that have signed the nuclear Non-proliferation Treaty.

The deal also commits Washington to persuade countries in the 44-member Nuclear Suppliers Group to lift restrictions on India in the civilian nuclear technology trade.

"For any agreement to be credible with the US Congress and the Nuclear Suppliers Group, it will have to be a detailed agreement, a substantial agreement," Burns said.

"It is a unique agreement. It has not been done before. India is a unique country," he added.

Saran last month gave Washington a plan to separate India's civil and military nuclear facilities, an Indian official said.

He said he was hopeful that the deal would get through the US Congress.

"Whatever interaction we have had so far leads us to believe that there is a lot of goodwill."

"There is a pervasive feeling of bipartisan support for India-US relations."

Some US lawmakers have questioned the wisdom of providing atomic fuel and technology to a nuclear power like India that has refused to sign the nuclear Non-Proliferation Treaty.

They also see India's response to Iran's suspected efforts to build nuclear weapons as key to the closure of the deal.

Saran, however, dismissed the suggestion.

"The cooperation agreement stands on its own merit," he said.

He said that India had a longstanding relationship with Iran and that it would not like to see any confrontation in the region.

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