Washington: As leaders from 50 nations began arriving for the Nuclear Security Summit here, the US said "India has a very important role to play with respect to responsible stewardship of nuclear weapons and nuclear materials." Meeting in the shadow of Brussels and Lahore terror attacks, Prime Minister Narendra Modi and other leaders will over the next two days discuss how to prevent terrorists and other non state actors from gaining access to nuclear materials and technologies. President Barack Obama, hosting the fourth and last such gathering, "obviously" is "delighted that Prime Minister Modi is able to be in Washington for the Nuclear Security Summit," Secretary of State John Kerry said before a meeting Wednesday with Indian National Security Advisor Ajit Doval. Doval, in turn, said India attached "considerable value" to this "very, very important summit and Modi "is deeply interested in seeing and ensuring that the safety and security of the radioactive material must be ensured." "India has a long record of being a leader, of being responsible," said Kerry. "And it is particularly important right now at a time when we see in the region some choices being made that may accelerate possible arms construction, which we have serious questions about." "We've raised them with various partners in the region. So our hope is that this Nuclear Security Summit will contribute to everybody's understanding about our global responsibilities and choices," Kerry said. Obama, America's top diplomat noted, "has called the relationship with India a defining relationship of this century, and there are many reasons for that." "India - a powerful, big, the largest democracy in the world, and a real partner with the United States on a lot of technology, energy issues," "We're particularly grateful to India for the leadership it offered in Paris helping us to reach a climate agreement," Kerry said. "And now, there is more that we can do with respect to the next steps in that agreement." Kerry said there were a number of other security and key issues "we need to talk about, but it's important to have this conversation." Doval said India and US "have made many strides after the new government of Prime Minister Modi has come and we have taken our relationship to new heights." "We have got many areas in which we have been able to improve and achieve substantial results," he said. "We do hope that this cooperation will find a new strength and new height, will get further strengthened and deepened." India, Doval said, "shared many concerns, particularly concerns about terrorism, concerns about the cyber space and we'll be working together on that." "We do hope that together, we should be able to make this place a better place to live and meet with these challenges together, and in cooperation with all other likeminded countries," he said. "We are all very proud and very happy about our good relationship and excellently growing relationship with United States," Doval added. Earlier Tuesday, Doval discussed counterterrorism cooperation, including against Pakistan based groups Lashkar-e-Taeba and Jaish-e-Mohammed, responsible for Mumbai and Pathankot terror attacks with US NSA Susan E. Rice at the White House. Modi who is making his third visit to the US in two years reflecting the transformation in India-US ties is expected to have a separate bilateral meeting with Obama on the sidelines of the summit. He was also expected to meet with his Pakistani counterpart Nawaz Sharif, but the latter has cancelled his Washington visit in the wake of Lahore attacks.