NASA is trying to resolve an international spat over banning Chinese scientists from a planetary conference but efforts are being hampered by the US government shutdown, a meeting organizer said Wednesday.

Some leading US astronomers have vowed to boycott the conference next month at a US space agency facility in California because six Chinese scientists were told they could not attend.

Beijing's foreign ministry has also described the move as discriminatory, and said academic meetings should remain free of politics.

Organizers of the Second Kepler Science Conference on November 4-8 said they were acting based on a March 2013 order for a moratorium to visits to NASA facilities by citizens of several nations including China.

The basis for the ban was called into question on Tuesday by Congressman Frank Wolf, who authored related legislation in 2011 that he said restricted space cooperation with the Chinese government and Chinese companies but not individuals.

The moratorium and other additional security measures were issued earlier this year by NASA administrator Charles Bolden following a potential security breach at a NASA facility in Virginia by a Chinese citizen, and should have been lifted by now, Wolf said.

Several attempts by AFP to reach NASA spokespeople have gone unanswered.

"The NASA folks are not legally able to read their e-mails. This is the major reason the brouhaha continues, in my opinion," said conference co-organizer Alan Boss of the Carnegie Institution for Science, in an email to AFP.

The US government shutdown, in place since October 1 over Republican opposition to President Barack Obama's health care reform, has sent 97 percent of the space agency home without pay along with hundreds of thousands of federal workers across the country.

"Representative Wolf's statement has caught the attention of NASA officials, who are working now to see if the problem can be solved," Boss told AFP.

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Shutdown slows bid to fix NASA-China controversy