Indian External Affairs Ministry said on Thursday that no particular date had been fixed for the visit by US Under Secretary of State Nicholas Burns to New Delhi. But US said after Indian Foreign Secretary Shivshanker Menon's trip to Washington earlier this month that Burns would be travelling to India by the end of May.

India and the US have exchanged drafts of the proposed agreement to operationalise the nuclear deal and both sides are trying to fine tune the language of the contentious provisions in the civilian nuclear deal, which is acceptable to the two sides, sources here said.

The differences by and large centre around India's right to reprocess nuclear fuel to be supplied to its civilian reactors and the controversial issue of whether India would continue to get nuclear materials if it tests another nuclear device.