North Korea is bolstering its coastal defenses and preparing to launch another long-range missile, believed to be capable of reaching Alaska, from a new base on its west coast, reports said Monday. South Korean news reports said North Korea has transported its most advanced missile, which is believed to be able to reach Alaska or Guam, to a newly completed launchpad on its western coast near China. According to Yonhap news agency, South Korea is also scrutinizing an intelligence report that the North has ordered troops in charge of the disputed western sea border and along the west coast to double their stocks of ammunition. Yonhap cited an unnamed government official as saying that the activity of vehicles to and from military bases along the coast has increased. The Defense Ministry declined to confirm the report. South Korean President Lee Myung-bak, hosting a conference of Southeast Asian leaders on the southern island of Jeju, warned North Korea against any provocation. "If North Korea turns its back on dialogue and peace and dare to carry out military threats and provocations, the Republic of Korea will never tolerate that," Lee said in his regular radio address. "I want to make clear that there won't be any compromise on things that threaten our nation's security." Lee said the North should understand that its nuclear threat to world peace threatens the regime itself. The new missile could be ready to launch as soon as mid-June, and might be ready in time for a summit between Lee and President Barack Obama on June 16, according to the Dong-a Ilbo newspaper. Timing the launch to coincide with the summit would be seen as an attempt to steal the spotlight from Lee and for North Korea to thumb its nose at attempts in the UN Security Council to rein it in after its nuclear test last week and a series of short-range missile launches it has already conducted. North Korea also has custody of two American journalists, Laura Ling and Euna Lee, accused of entering the country illegally and engaging in "hostile acts." Their trial begins Thursday in Pyongyang. North Korea faced strong international criticism after its last long-range missile launch, on April 5. The North, however, countered that launch was of a peaceful rocket intended to put a satellite in orbit. In another sign that a launch is in the works, the North has designated a large area off its west coast as a "no-sail" zone through the end of next month, the Chosun Ilbo newspaper said, citing unidentified intelligence officials. Seoul's Defense Ministry declined to confirm these reports, saying it does not comment on intelligence matters. But a defense official confirmed Sunday that US satellites had detected preparations to transport a missile for a test launch. Experts said the preparations for the launch were especially significant because the North has never launched a long-range missile from the northwestern base. Kim Tae-woo, vice president of Seoul's state-run Korea Institute for Defense Analyses, said he thinks the North chose the new missile site because of its proximity to China, making it more risky for the US to strike. The site is about 60 kilometers from the Chinese border city of Dandong. Kim also said the North could be trying to diversify its missile operations. "From the Dongchang-ni site, it can fire a missile southward across the Yellow Sea," he said. The North's Taepodong-2 rocket flew about 3,200 kilometers on April 5, crossing over Japan and crashing into the Pacific Ocean. The missile being readied for a new launch is believed to be an intercontinental ballistic missile with a range of up to 6,500 kilometers, the JoongAng Ilbo reported, citing an unnamed South Korean official. That would put Alaska within striking range. In late April, the North had threatened to conduct nuclear and long-range missile tests unless the UN Security Council apologized for criticizing its rocket launch. Pyongyang conducted an underground atomic blast last week. On Friday, it also threatened to take a further "self-defense" measure if it is provoked by the Security Council. That threat was seen as referring to an ICBM test. On Monday, the North said again that it is being provoked by South Korea and the United States, saying that the number of spy planes operating in its airspace has risen dramatically. "The US imperialists and the South Korean puppets perpetrated at least 200 cases of aerial espionage against the DPRK in May, or 30 cases more than those in the same month of last year," it said in a report in its official Korean Central News Agency. The DPRK is an abbreviation of North Korea's official name. On Yeongyeong island, one of South Korea's northernmost islands near North Korea, South Korean naval boats and a warship were patrolling waters around the disputed western sea border, but no incidents were reported. The area is rich in fish, and May and June are the crab catching season. North Korea has been building the new launch site at Dongchang-ni for years. Last year, Seoul's Defense Minister Lee Sang-hee told parliament that its construction was about 80 percent complete. Monday's newspaper reports said that the construction is near completion. The North's missile and nuclear programs have been considered a top security concern for the region, though the regime is not yet believed to have mastered the technology to make a nuclear warhead small enough to mount on a missile. North Korea conducted its first nuclear test in 2006. International negotiations aimed at ridding the North of nuclear capabilities have been stalled since last year.