MOSCOW, May 26 (UPI) -- A U.S.-based British businessman who had promised to pay $100 million toward the upkeep of Russia's 13-year-old Mir space station in exchange for a flight to Mir has bailed out of the plan, quitting a training program for cosmonauts at Star City near Moscow and abruptly leaving Russia, Russian space officials say. Russian space officials told United Press International they regretted the turn of events, while the deputy chief of the cosmonaut training program, Andrei Maiboroda, told Russia's Itar-Tass press service Peter Llewellyn had ``turned out to be an unreliable partner.'' The cash-strapped Russian space program had pinned hopes on receiving much-needed funds from Llewellyn, a 51-year-old businessman, and Mir's future is now in jeopardy as state funding will run out in August, when the last cosmonauts are scheduled to abandon the station. Until this week, Russian officials the plan was going ahead, despite notes of caution in the media over Llewellyn's creditworthiness and a recent warning from Russian President Boris Yeltsin that the Mir program would not receive additional state funding and would have to rely solely on commercial deals to continue operating. Officials at RKK Energiya, which operates Mir, say Llewellyn had agreed to transfer the money to the space program, while the businessman insisted last month that he was collecting money for construction of a children's hospital in Russia and the space flight would be a sign of gratitude from Russia. Now that Llewellyn has bailed out, Russian Space Agency officials tell UPI they will concentrate on the international space station project, which will in effect mean abandoning Mir. However, some still hope the station can be saved and kept in orbit for a few extra years. Boris Ostroumov, deputy director general of the Russian Space Agency, said on Tuesday: ``It just doesn't make much sense to get rid of such a treasure.'' Ostroumov said that while government funding of Mir will run out in August and the last crew will return to Earth, the station's orbit is expected to be stable with no additional fuel needed from Earth until February 2000. He said Mir could be left untended but in orbit for several more months after the August deadline. Said Ostroumov: ``We all understand that no matter how bad we feel about it, we cannot support two programs at the same time....Any funds that are allocated will be used exclusively for the International Space Station.'' Russian delays in building the new station's core module have raised questions about a possible conflict of interest between maintaining Mir and building the new station. However, Ostroumov reiterated the International Space Station is Russia's top priority.  