SEOUL (AFP) - Two days after North Korea's nuclear test, South Korea signalled Thursday the deployment of a new cruise missile capable of a precision strike on members of Pyongyang's high command.The defence ministry called in reporters for a special video presentation of the recently deployed missile being fired from a warship and a submarine."The cruise missile unveiled today is a precision-guided weapon that can identify and strike the office window of the North's command headquarters," ministry spokesman Kim Min-Seok told reporters.It has "deadly destructive power" that could "restrain the enemy headquarters' activities" during wartime, Kim said. South Korea's military has been on a heightened state of alert ever since Pyongyang first threatened the nuclear test which was eventually conducted on Tuesday.It was the North's third test, following previous detonations in 2006 and 2009, and seismic data suggested it was significantly more powerful.The test appears to have galvanised South Korea into flexing its military muscle and highlighting its own technological prowess. "With this missile, we could hit any facility, equipment or individual target in the North anywhere, at any time of our choosing," army Major General Ryu Young-Jeo said of the cruise missile. On Wednesday, South Korea said it would accelerate the development of longer-range ballistic missiles that could also cover the whole of North Korea.In October last year, South Korea reached a deal with the United States to almost triple the range of its ballistic missile systems - with Seoul arguing it needed an upgrade to counter the North's own missile development.The United States has 28,500 troops in South Korea and guarantees a nuclear "umbrella" in case of any atomic attack. In return, Seoul accepts limits on its ballistic missile capabilities.The defence ministry also said it would speed up the deployment of a "kill chain" system capable of detecting, targeting and destroying North Korean missiles.Urgent efforts to find out the type of device detonated in North Korea's latest nuclear test appeared to be getting nowhere Thursday, with South Korean experts unable to detect any radioactive fallout. The North's test on Tuesday triggered an immediate scramble to collect and analyse any fallout data that might provide crucial clues about the nature of the test and the progress Pyongyang's nuclear weapons programme has made.Experts are particularly keen to establish whether the North switched from plutonium - used in the 2006 and 2009 tests - to a new and self-sustaining nuclear weaponisation programme using highly enriched uranium. The South's state-run Nuclear Safety and Security Commission said Thursday it had analysed eight atmospheric samples apparently collected by warships and air force planes equipped with highly sensitive detection devices. "No radioactive isotope has been found yet," the commission said in a statement.Their priority target was traces of xenon gases released in the detonation that would point to the weapon type. "We are analysing samples and xenon has not been found," the commission statement said. If the underground test was well contained, it is quite possible there would be little or no radioactive seepage into the atmosphere.A Seoul government source quoted by Yonhap news agency suggested that was the case, saying the entrance to the tunnel where the test was conducted remains intact. And even if some gases did escape, scientists stress there is a large amount of luck involved in collecting them. No xenon gases were detected after the North's 2009 test. As well as the military detectors, the commission said there were 122 automated devices across South Korea that were continually capturing and analysing air samples.The detection effort is running on a very tight deadline. Xenon-133m, a metastable isotope needed to pin down the fissile material type, has a half-life of just over two days.Proof of a uranium test would confirm what has long been suspected: that the North can produce weapons-grade uranium, doubling its pathways to building more bombs in the future.The North has substantial deposits of uranium ore and it is much easier secretly to enrich uranium in centrifuges rather than enriching plutonium in a nuclear reactor.