Both sides sounded upbeat after two days of talks here between top US State Department official Nicholas Burns and Indian Foreign Secretary Shivshankar Menon, which were aimed at implementing a July 2005 accord on atomic energy.

Burns, the US under secretary of state for political affairs, will travel to India "in the second half of May to reach a final agreement," State Department spokesman Sean McCormack said after what he termed "excellent" meetings.

"We look forward to resolving the outstanding issues in the weeks ahead," he said in a statement, arguing that Menon's talks with officials including Secretary of State Condoleezza Rice had yielded "extensive progress."

Menon would not be tied down on a date to wrap up the landmark nuclear pact but said ahead of Burns' visit: "As far as I'm concerned, this is doable ... and we want to do it as quickly as possible."

The US government had expressed frustration over the pace of the talks to implement the pact, which would give India access to US nuclear energy technology without requiring the Asian country to halt its atomic arms programme.

The deal is the centrepiece of energy-hungry India's new relationship with Washington after decades of Cold War tensions, as it tries to sustain its stunning economic expansion.

"I think it's a measure really of how the relationship has been transformed in the last few years," Menon said.

As India deepens free-market reforms and attracts billions of dollars in investment, the United States sees the emergence of a democratic ally and a bulwark against instability in a restive, nuclear-armed region.

In an opinion piece in Sunday's Washington Post, Burns predicted that "within a generation, Americans may view India as one of our two or three most important strategic partners."