WASHINGTON - Ahead of the Nuclear Security Summit, the US has said that Pakistan takes its responsibility for securing its nuclear stockpile "very seriously".

"Without question, Pakistan takes very seriously its responsibility to provide security for both nuclear weapons and nuclear materials. As a consequence of the summit process as well as our bilateral cooperation they have taken important steps forward in providing that security," US Assistant Secretary of State for International Security and Nonproliferation Thomas Countryman told reporters.

He was responding to a question from an Indian journalist who asked whether Washington thought the Pakistani nuclear weapons were safe in view of the high-profile terrorist attacks that have taken place in the country.

"Islamic State, of course, would like to get its hand of weapons of mass destruction," Countryman said in response to a question from the same journalist.

"At the moment, thanks to the important steps that have been taken by countries throughout the region as well as the fact that the international coalition is pushing back Islamic State, the threat is not immediate from Islamic State seeking nuclear weapons, but it is not an issue that we ever ignore or take for granted," he said.

Noting that Pakistan is part of the NSS from the very beginning and that they have been part of the process of securing nuclear materials and weapons, US Coordinator for Threat Reduction Programmes Bonnie Jenkins said Pakistan takes this issue seriously.

Jenkins, who was recently in Pakistan to visit its center of excellence, said the International Atomic Energy Agency hosted a meeting there for a network of centers of excellence who work together and learn from each other and share best practices.

"We had the first meeting of this network outside Vienna, where IAEA is located in Islamabad. We had a chance to visit their center of excellence, went to their nuclear regulatory authority … it showed what they are doing in terms of training on issues of nuclear security," she said.

Pakistan, she said, recently ratified the 2005 amendment to Convention on Physical Protection of Nuclear Material (CPPNM).

The two-day Nuclear Security Summit would be attended by heads of State of more than two dozen countries including Prime Minister Narendra Modi, but Prime Minister Mian Muhammad Nawaz Sharif will not participate in view of the deadly terrorist attack in Lahore.