North Korea is assembling a long-range missile capable of reaching Alaska, a news report said on Wednesday, as the communist regime prepared to test-fire a barrage of missiles from both coasts. The moves further heightened tensions in the region following North Korea's underground nuclear test last week, and came as speculation grows that leader Kim Jong Il has selected his third son as heir to the communist dynasty. At the border village of Panmunjom inside the Demilitarized Zone separating the two Koreas, a military guide warned tensions are running deep. The possibility of armed provocation is higher than ever in the Joint Security Area,'' said the South Korean military guide taking journalists on a tour of the border area. He did not provide his full name saying he did not have permission to do so. The guide also cautioned journalists not to point at the North Koreans or make any gestures.'' On the North Korean side of the area, a lone guard could be seen standing with his arms to his side, just watching the journalist group. The mass-market JoongAng Ilbo newspaper said on Wednesday that a long-range missile _ transported by train to the Dongchang-ni launch site near the North's northwest coast near China _ is believed to have entered an assembly building. The paper cited an unnamed South Korean official saying the missile was covered up and a little longer than the Taepodong-2 rocket the North fired on April 5. An American military official confirmed an intercontinental ballistic missile capable of striking the U.S. was being readied at a base on the North's west coast. The official said it could be more than a week before Pyongyang was ready to launch. He spoke on condition of anonymity because it was an intelligence-related issue. Separately, North Korea may soon launch three or four mid-range missiles, believed to be modified versions of its Rodong series, from its east coast, South Korea's Yonhap news agency reported. The U.N. Security Council is considering measures to punish the North for the nuclear test, and U.S. Deputy Secretary of State James Steinberg said after meeting with South Korean Vice Foreign Minister Kwon Jong-rak he still has hope the North will change course.