A high-level Indian delegation, led by National Security Advisor M K Narayanan, currently in the US to iron out difference over the implementation of the Indo-US civilian nuclear deal, held talks with senior American functionaries on bilateral defence cooperation and regional security issues.

The US side was led by Secretary of State for Defence Robert Gates.

Besides Narayanan, other members of the Indian delegation included Ambassador of India to the United States Ronen Sen, Foreign Secretary Shivshankar Menon, Deputy Chief of the Indian Mission here Raminder Singh Jassal and Joint Secretary of the Americas of the Ministry of External Affairs Gaitri Kumar.

While the precise nature of the Monday night talks was not divulged, sources said the two sides exchanged frank and candid views on bilateral defence cooperation and regional and other security issues.

The Indian delegation is in Washington for four days of sensitive and critical exchanges with their American counterparts focussing primarily on the civilian nuclear cooperation agreement, especially nailing of the 123 Agreement.

But members of the Indian delegation, collectively and individually, will be meeting senior officials of the Bush administration on issues pertaining to the broader aspects of the bilateral relationship as well.

"There is more to India-United States relations than the civilian nuclear agreement," remarked a source when asked for the rationale of the top Indian delegation meeting with the US Secretary of Defence.

The crux of the meetings on the civilian nuclear deal will start at the State Department on Tuesday afternoon when the Indian Foreign Secretary and his delegation will be meeting the Under Secretary of State for Political affairs Nicholas Burns with a view to sorting out the remaining differences on the 123 accord.

Menon's delegation for the talks will include Indian Ambassador in Washington, his deputy, India's High Commissioner to Singapore Jaishankar and the Joint secretary of the Americas Kumar.

Burns will have his delegation as well which will include Robert Stratford and his team dealing with the 123 Agreement and Richard Boucher, the Assistant Secretary of State for South and Central Asia.

Sources told PTI that Menon and Burns will have ample opportunities to discuss the nitty-gritty of the 123 Agreement in formal sessions and otherwise.

The main and perhaps the most important meeting will be in the White House on Wednesday between Narayanan and his US counterpart Stephen Hadley, the US National Security Advisor to the President.

The format for this meeting is a one-on-one as well as delegation-to-delegation exchange of views.

Sources said that the two main issues on the 123 Agreement separating the two sides have to deal with reprocessing and right of return of materials, equipment and fuel in case the civilian nuclear deal comes to an end with India deciding to conduct a nuclear test.

"These are important issues and it is going to take time to sort out," the sources told PTI.