ENNISKILLEN, Northern Ireland — President Barack Obama and Russian President Vladimir Putin said they would sign an agreement on securing and destroying nuclear material to prevent the spread of nuclear weapons, replacing a 1992 deal that expired on Monday. Obama and Putin met privately at the G8 summit to talk about pressing security issues and agreed to work together to protect, control and account for nuclear weapons. “I think it is an example of the kind of constructive, cooperative relationship that moves us out of a Cold War mindset,” Obama said after meeting with Putin. Ben Rhodes, a spokesman for the National Security Council, said Russia had been reluctant to extend the agreement, which was signed after the collapse of the Soviet Union and was known as the Nunn-Lugar agreement after former Democratic Senator Sam Nunn and former Republican Senator Richard Lugar. Rhodes said the Russians' concerns were “well founded in some respects,” noting the Nunn-Lugar agreement had taken a “very aggressive and intrusive” approach to securing nuclear material in Russia. On Monday, Nunn applauded the new deal, although he noted that some parts of the old one focused on chemical and biological weapons would not continue. “We must find ways beyond this agreement to work together on these critical issues,” he said. “I believe that we will.” — Reuters