"One of the challenges that we're going to have here is that it is very difficult to see huge reductions in our nuclear arsenal unless the United States and Russia, as the two largest possessors of nuclear weapons, are prepared to lead the way," Obama said.
"The other area where I think we need to see progress is Pakistan and India, that subcontinent, making sure that as they develop military doctrines, that they are not continually moving in the wrong direction," he told a press conference at the end of the two-day Nuclear Security Summit here.
"We have to take a look at the Korean Peninsula because North Korea is in a whole different category and poses the most immediate set of concerns for all of us, one that we are working internationally to focus on," he said.
Obama said this was one of the reasons he had a trilateral meeting with Japan and Korea, adding that it was a major topic of discussion with his Chinese counterpart Xi Jinping as well.
Obama's remarks are seen in the context of growing American uneasiness about the rapidly increasing nuclear arsenal of Pakistan.