The United States and India on Tuesday said they had made “extensive progress” in talks to iron-out differences over a civilian nuclear deal, and American officials expressed optimism that a “final agreement” would be reached later this month.

Foreign Secretary Shiv Shankar Menon and Under Secretary of State R. Nicholas Burns on Tuesday wrapped up talks, which had started over dinner on Monday. Menon later said he was “happy” with the “very productive discussions.”

He added: “As far as I’m concerned, this is doable ... and we want to do it as quickly as possible.”

State Department spokesman Sean McCormack issued a written statement saying the meetings “were positive and the US is encouraged by the extensive progress that was made on the issues.”

“We look forward to resolving the outstanding issues in the weeks ahead,” McCormack said, adding, Burns would visit India in the second half of May “to reach a final agreement.”

Menon also had an “excellent meeting” with Secretary of State Condoleezza Rice on Tuesday.

In a notable about-face from their recent practice of venting frustrations in the press, both sides on Tuesday refused to divulge details of how seemingly insurmountable differences had been resolved overnight. The shroud of secrecy was the result of an understanding between both sides that public airing of grievances would only strengthen foes of the deal in Washington and New Delhi.

Going into the talks, major differences existed on the 123 agreement over nuclear testing and reprocessing rights. The draft says the US will cease nuclear cooperation with India, if India conducts a nuclear test. India also will not be allowed to reprocess spent nuclear fuel. India, which has refused to sign the Comprehensive Test Ban Treaty and is under no legal obligation not to test, has opposed a testing ban.

In a report tabled in Parliament in New Delhi last week, Menon assured critics of the deal that, “Whatever we do with the US will not affect our nuclear strategic programme.”

McCormack, who spoke with Burns following the under secretary’s dinner meeting with Menon on Monday, said the foreign secretary had come to Washington with “some constructive ideas.”

Before the agreement is implemented the US Congress must ratify the final terms of the deal; the International Atomic Energy Agency has to approve a separate nuclear inspection programme; and the Nuclear Suppliers Group has to approve the deal.

Some members of Congress ratcheted up their criticism of the agreement even as Menon was meeting with Burns. They also expressed concern about India’s ties with Iran.