U.S. space agency NASA said Wednesday that it has suspended the majority of its engagements with Russia due to the Ukraine crisis.

However, NASA and its Russian counterpart Roscosmos will continue to work together to maintain the safe and continuous operation of the International Space Station (ISS), the space agency said in a statement emailed to Xinhua.

There are currently three Russians, two Americans and one Japanese aboard the ISS.

Earlier, an internal letter published by U.S. space news website Spaceref said that the U.S. government had determined that all NASA contacts with the Russian government representatives are suspended "unless the activity has been specifically excepted."

"This suspension includes NASA travel to Russia and visits by Russian government representatives to NASA facilities, bilateral meetings, email, and teleconferences or videoconferences. At the present time, only operational International Space Station activities have been excepted," the letter said.

In addition, multilateral meetings held outside Russia that may include Russian participation are not precluded under the present guidance, it added.

In March, NASA Administrator Charles Bolden repeatedly said that space cooperation between the two countries would not be affected by tensions over Ukraine.

"Right now everything is normal in our relationship with the Russians," Bolden said on March 4. "Since the International Space Station has been in orbit, it's very important to understand that started a partnership between the United States and Russia. That partnership remains intact and normal."

Scott Pace, director of George Washington University's Space Policy Institute, told Xinhua that the instructions given to NASA are consistent with instructions given to all other government agencies regarding bilateral cooperation with Russia, with the exception made for the ISS.

Multilateral government activities will continue, such as participation in international organizations, he said.

When asked about the possible consequences, Pace said he "would expect that the major impacts will be to bilateral scientific cooperation."

"I don't see how this really benefits the U.S. or punishes Russia, but NASA needs to conform to the constraints imposed on all other U.S. agencies," he added.

It is unclear how Russia will respond to the ban. Joan Johnson-Freese, a professor of national security affairs at the U.S. Naval War College, told Xinhua that the possibility cannot be totally excluded that President Vladimir Putin could decide to use ISS access as "a political tool."

NASA is currently totally dependent on Russian spacecraft to ferry astronauts to the ISS and back after retiring the Space Shuttle in 2011, and it hopes to change this within the next four years by using commercial spacecraft currently under development.

In Wednesday's statement, NASA stressed that it is committed to ending its reliance on Russia to get into space. The space agency also said it would have returned American human spaceflight launches back to the United States next year had its commercial crew program been fully funded by Congress.

"With the reduced level of funding approved by Congress, we're now looking at launching from U.S. soil in 2017," it said.

"The choice here is between fully funding the plan to bring space launches back to America or continuing to send millions of dollars to the Russians. It's that simple. The Obama administration chooses to invest in America -- and we are hopeful that Congress will do the same," it added.

Source: Xinhuanet