New Delhi: In a "breakthrough", India and the US Sunday agreed to move towards "commercial cooperation" as well as "full implementation" of their landmark civil nuclear deal.

The announcement was made by US President Barack Obama and Prime Minister Narendra Modi, brightening the prospects of the deal that was inked during the Manmohan Singh regime in 2008 but never implemented.

"The civil nuclear agreement was the centrepiece of our transformed relationship, which demonstrated new trust. It also created new economic opportunities and expanded our option for clean energy," Modi said addressing a joint press conference with Obama here.

"...I am pleased that six years after we signed our bilateral agreement, we are moving towards commercial cooperation, consistent with our law, our international legal obligations, and technical and commercial viability."

Describing it as a "breakthrough understanding", Obama said the two leaders agreed to "advance our civil nuclear cooperation and we are committed to moving toward full implementation".

"It is an important step and shows us how we can work together to elevate our relationship."

Modi and Obama met at Hyderabad House for a marathon four-hour-long session of summit-level talks, their second in the last four months after the one during the prime minister's maiden visit to the US in September 2014.

Obama, accompanied by his wife Michelle, is here to attend the 66th Republic Day parade as chief guest.