The threat of a nuclear conflict between the United States and North Koreaaffected an event marking the anniversary of world's second atomic attack.A crowd gathered in the Japanese city of Nagasaki Wednesdayto remember the U.S. atomic bombing there in the final days of World War II.The attack took place on August 9, 1945.Three days earlier, U.S. forces had dropped an atomic bomb on the Japanese city of Hiroshima.The mayor of Nagasaki spoke at Wednesday's observance.He said "A strong sense of anxiety is spreading across the globethat in the not too distant future these weapons could actually be used again."He and the crowd observed a moment of silence at 11:02, local time-- the exact time when the atomic bomb was dropped.The ceremony took place a short time after U.S. and North Korea officialsexchanged strong language about the North's nuclear activities.On Tuesday, American media reported that the U.S. Defense Intelligence Agencythinks North Korea recently succeeded in building a small nuclear warhead.The weapon is said to be small enough for the missiles that North Korea recently test-fired.The North Korean government has threatened nuclear war with the United States in the pastbecause of United Nations sanctions against North Korea.Those measures are meant to punish the government for its nuclear tests.U.S. President Donald Trump warned North Korea Tuesdaythat its threat against the United States"will be met with fire and fury like the world has never seen."North Korea reacted quickly to Trump's comments.The North's Korean Central News Agency saidthe North Korean military is examining its planfor "making an enveloping fire" around Guam.The U.S. military has bases on the island territory.This is the first time that North Korea has identified an exact target.Balbina Hwang teaches at Georgetown University in Washington, D.C.She said, "The increase in rhetoric does raise existing tensions,but it does not translate into a shift of U.S. policy or strategy on North Korea."A former deputy U.S. ambassador to the UN, David Pressman,is concerned about the rising tensions."Perhaps there wasn't a careful consideration of the wordsof our commander in chief in this instance," Pressman said.He added that, "If ever there was a topic on which we needto be extremely precise, it's nuclear proliferation,when dealing with someone who is as unpredictable as Kim Jong Un."Speaking to reporters while flying to Guam,U.S. Secretary of State Rex Tillerson saidhe does not believe there is a threat to the island any time soon.He added "the president is sending a strong message to North Koreain language that Kim Jong Un would understand."In Seoul, South Korean officials seem to agree with Tillerson's comment.A top official said "I do not believe the situation has reached a state of crisis,and rather think we may turn this into an opportunityto overcome the serious security condition."The South Korean news agency Yonhap reported his comments.