In the mid-90's, the Japanese nerve gas cult Aum Shinrikyo was for a while suspected of testing a nuke in the Australian outback. From The New York Times (story from 1997):
Senate investigators found that the group had thousands of disciples in Russia and had bought guns, a military helicopter and other weapons there. The group's construction minister, Kiyohide Hayakawa, the reputed mastermind of the cult's efforts to arm itself, went to Russia 21 times from 1992 to 1995, visiting there a total of 180 days.
Senate investigators say the cult recruited at least two nuclear scientists in Russia.
Notebooks later seized from Mr. Hayakawa show he wanted to buy the ultimate munition there. In one entry, he asked, ''How much is a nuclear warhead?'' and listed several prices.
In Australia, the activities were just as troubling. Cult members arrived in April 1993, a little more than month before the mystery blast. Mr. Hayakawa, apparently fresh from visits to Russia, was among the initial party. After visiting several remote sites, the group bought a 500,000-acre sheep farm in Banjawam, Australia, about 400 miles northeast of Perth. The site has a known uranium deposit.
The cult eventually brought in chemicals, gas masks and respirators, and picks, shovels, mining equipment and a mechanical ditch digger. It also set up a laboratory stocked with computers, glass tubing, glass evaporators, beakers, Bunsen burners, mixing bowls and a rock-crushing machine.
Documents seized from Mr. Hayakawa include some 10 pages written during his visit to Australia in April and May 1993 that refer to the whereabouts of Australian properties rich in uranium, including one reference praising the high quality of the ore.
The disturbance shook the earth on May 28, 1993, at 11:03 P.M. local time, but it was not until after the Tokyo attack of March 1995, that an Australian geologist, Harry Mason, brought the seismic upset to the attention of Australian Federal Police and Senate investigators. He was prompted in part by public disclosures in June 1995 of uranium mining at the cult's ranch.