Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. President Obama: Risk of Nuclear Attack Increased VOA News 13 April 2010 President Barack Obama talks with German Chancellor Angela Merkel, left, and Singapore Prime Minister Lee Hsien Loong, right, during the opening plenary session at the Nuclear Security Summit in Washington, 13 Apr 2010 Photo: AP President Barack Obama talks with German Chancellor Angela Merkel, left, and Singapore Prime Minister Lee Hsien Loong, right, during the opening plenary session at the Nuclear Security Summit in Washington, 13 Apr 2010 U.S. President Barack Obama says the risk of a nuclear attack has increased as terrorists seek nuclear materials. Speaking Tuesday on the final day of a two-day nuclear summit, the president said even though the threat of nuclear war between nations has decreased, terrorist groups like al-Qaida are working to acquire nuclear materials. Mr. Obama said the new nuclear threat facing the world after the end of the Cold War is a "cruel irony of history." He warned that world leaders must act now and not simply talk about securing nuclear materials.  The 47 countries participating in the summit in Washington are expected to issue a joint declaration pledging to secure materials over the next four years. The president also announced Tuesday that South Korea will host the next nuclear summit in two years. Mr. Obama will hold one-on-one meetings later Tuesday with Turkish Prime Minister Recep Tayyip Erdogan, Argentine President Cristina Fernandez de Kirchner and German Chancellor Angela Merkel. U.S. Secretary of State Hillary Clinton is to sign a protocol with Russia Tuesday on eliminating excess weapons-grade plutonium from defense programs. Before the start of the summit Monday, Mr. Obama met with Chinese President Hu Jintao, with Beijing agreeing to work with Washington on possible sanctions on Iran for its controversial nuclear activities. China has been reluctant to place more U.N. sanctions on Tehran. Iran, North Korea and Syria, much criticized by the West for their suspected nuclear programs, were not invited to the summit. Mr. Obama also held talks Monday with Ukrainian President Viktor Yanukovich. The White House then announced that Ukraine will get rid of its stockpile of highly enriched uranium by 2012. Canadian Prime Minister Stephen Harper announced Canada will return large inventories of enriched uranium to the United States to keep them out of the reach of terrorists. Some information for this report was provided by AP, AFP and Reuters. .