STAR CITY, Russia (Reuters) - Russia announced a halt to space tourism on Wednesday, saying it would struggle to ferry professional crews to the International Space Station after the U.S. mothballs its shuttle fleet this year.

Ground crew members assist Canadian circus billionaire Guy Laliberte after he returned in the Russian Soyuz space capsule near the town of Arkalyk, in northern Kazakhstan, October 11, 2009. REUTERS/Yuri Kochetkov/Pool

NASA plans four more shuttle flights to the $100-billion, 16-nation space outpost before retiring its three shuttles by the end of the year.

Russia, sending crews to the ISS aboard its single-use three-man Soyuz ships, will double the number of manned launches to four this year because permanent crews of professional astronauts aboard the expanded station are set to rise to six.

“This year will see the last shuttle mission, and from this moment Russia will not only become the sole nation sending crews, but ... also the only country ensuring the crew’s safety,” Sergei Krikalyov, the head of the Russian Cosmonauts’ Training Center, told reporters in Star City outside Moscow.

“As for (space) tourists ... there are now going to be six crew members, and it will be impossible to ferry a tourist each time there is a new crew shift in orbit, and for some time there will be a break in these journeys,” Krikalyov said.

Canadian circus billionaire Guy Laliberte was the latest rich traveler -- officially the world’s seventh space tourist -- who visited the ISS briefly aboard a Soyuz last October after paying $35 million for his ride.

Russia plans to launch the first of this year’s planned four Soyuz ships on April 2. The U.S.-Russian trio will join a U.S.-Russian-Japanese team which has been manning the outpost since December.

Krikalyov did not say how long the break in space tourism would be. He made clear it would largely depend on how long it takes NASA to build a new space ship to replace the Shuttle.

He said the United States targets 2014 as the deadline for building the new space ship, but there could be delays.

“The talk will definitely be about years, but it’s hard to say now, whether it’s going to be one year, two years or five years,” Krikalyov said. “The creation and trial of new spacecraft involves great technical risk and huge uncertainty.”