By Cindy Wooden Catholic News Service VATICAN CITY (CNS) -- More than 50 years of papal and Catholic social teaching against nuclear weapons has given moral weight to a worldwide nonproliferation effort, said a U.S. disarmament expert who visited the Vatican April 10. Rose E. Gottemoeller, undersecretary of state for arms control and international security, was in Rome with Madelyn Creedon, principal deputy administrator of the National Nuclear Security Administration, for meetings with officials of the Pontifical Council for Justice and Peace, and the Pontifical Academy of Sciences and with Msgr. Antoine Camilleri, Vatican undersecretary for relations with states. The meetings focused on preparations for the Nuclear Nonproliferation Treaty Review Conference April 27-May 22 at the United Nations. Gottemoeller told reporters she "was excited and very glad" that Pope Francis in his formal Easter address mentioned the recently announced framework negotiated in Lausanne, Switzerland, for an eventual agreement ensuring Iran does not develop a nuclear weapon. The negotiations involved Iran and what is often referred to as the "P5+1," or the five permanent members of the U.N. Security Council -- China, France, Russia, the United Kingdom, and the United States -- plus Germany. "In hope we entrust to the merciful Lord the framework recently agreed to in Lausanne, that it may be a definitive step toward a more secure and fraternal world," the pope said April 5. The negotiations with Iran were already on the pope's radar in January when he met with diplomats accredited to the Vatican, Gottemoeller said. The pope had told the diplomatic corps, "I express my hope that a definitive agreement may soon be reached between Iran and the 5+1 group regarding the use of nuclear energy for peaceful purposes." "This is a big issue for the Vatican, for the Holy Father," Gottemoeller said. The goal of nuclear disarmament, she said, "is very much alive and kicking" and decades of Catholic teaching about "nuclear weapons, nuclear deterrence and commitment to disarmament is a very important moral impetus that I think can really help set the right environment for the review conference." Asked about the U.S. nuclear "modernization" program, Creedon insisted that it is not increasing the military capabilities or power of the remaining weapons in the American stockpile. "We have been dismantling what we had at the end of the Cold War," she said. "We've been engaged in a steady dismantlement program since the end of the Cold War." The U.S. nuclear arsenal contained 31,175 warheads in 1966, according to the Department of Defense. As of September 2013, the U.S. government had a stockpile of 4,804 warheads, according to a 2014 Federation of American Scientists report. "On the modernization side, not only is our stockpile much smaller, but it's also much older because there hasn't been a new nuclear weapon since the end of the Cold War," Creedon said. "What we are doing now is going through these life-extension projects, basically replacing old parts. We are making them more safe, more secure, but we are not giving them any new military capabilities and we are not making them bigger."