Tokyo, Aug 21, SPA -- A U.S. satellite has detected signs that North Korea recently restarted a reactor that could be used for the extraction of material to make nuclear warheads, Reuters quoted a Japanese newspaper as saying on Sunday. The surveillance satellite detected steam coming out of a boiler connected to a building housing the five-megawatt reactor at Yongbyon, Asahi Shimbun said, quoting unnamed sources related to six-way nuclear crisis talks, including a senior U.S. official. The sources said the steam had been detected before the resumption of the six-way talks in late July that aimed to entice the North to give up its nuclear weapons and bomb-making programmes in exchange for economic aid and security guarantees. "It is hard to think that the boiler would operate by itself while the nuclear reactor is stopped. It can only be concluded that North Korea has put in new nuclear fuel rods and has restarted the nuclear reactor," Asahi quoted a U.S. government source as saying. South Korea said in April the reactor's operations had been suspended and the following month, North Korea said it had completed extracting 8,000 fuel rods from the 5 megawatt reactor. Rods from old-style graphite reactors can be processed to extract plutonium, a key component in nuclear bombs. Restarting the reactor could mean the North aims to extract more plutonium from the new rods. North Korea said in February that it possessed nuclear weapons. North Korea has also spread gravel over a road near a separate unfinished 50-megawatt reactor at Yongbyon. Construction was halted in the 1990s under a previous, and now defunct, nuclear agreement with the United States. Repairing the road could be a sign the North is preparing to resume building work, Asahi said. --mor 1255 Local Time 0955 GMT www.spa.gov.sa/285627