As senior Indian and American officials grapple to try and seal an agreement on civilian nuclear cooperation, Prime Minister Manmohan Singh on Wednesday said the negotiations have entered the last leg.

"I can't say," was Singh's reaction to reporters queries on when the negotiations will be concluded.

"We are in last leg of negotiations," he said.

A high level Indian delegation led by National Security Advisor M K Narayanan on Tuesday began parleys to iron out differences over the implementation of the Indo-US civilian nuclear deal.

Indian and US officials were on Wednesday engaged in a fresh round of negotiations in Washington, with Washington saying though the deal was within reach, there are a couple of tough issues left to be resolved.