US space agency NASA said Monday that future manned spaceflights to the International Space Station (ISS) could save millions of dollars using spacecraft currently being developed by private US companies Boeing and SpaceX.

NASA's commercial crew program manager Kathy Lueders told a webcast press conference that the average cost to fly US astronauts on Boeing's CST-100 and SpaceX's Dragon from American soil in 2017 will be 58 million US dollars per seat, based on a five-year mission plan.

Right now, Russian space agency Roscosmos is charging NASA over 70 million dollars per seat to get US astronauts into space.

"In terms of the reliance on Russians, ... I don't ever want to have to write another check to Roscosmos after 2017," NASA administrator Charles Bolden said.

Boeing and SpaceX were selected in September 2014 to build their respective CST-100 and Dragon spacecraft along with the rockets that will lift them into orbit by 2017.

NASA has had to rely on Russia's Soyuz spacecraft to transport US astronauts to the ISS since the end of the space shuttle program in 2011.

Boeing said during Monday's conference that it will conduct a pad abort test in February 2017, followed by an uncrewed flight test in April 2017, then a flight with a Boeing test pilot and a NASA astronaut in July 2017.

If all goes well, Boeing's first services mission to the ISS will begin in December 2017, the company said.

California-based SpaceX has a slightly different plan, anticipating a pad abort test later this spring, then an uncrewed flight test in late 2016 and a flight test with crew in early 2017.

"Competition provides more options and flexibility for the agency throughout contract performance and it reduces overall risk to the program," Lueders said.

"I feel that when we have two robust systems flying our four crew members and the additional powered cargo to and from the station, and providing the lifeboat function, NASA and the nation will be the winners," she added.