China has made dramatic improvements in its military capabilities in space, according to a senior US general.
General Kevin Chilton, commander of US Strategic Command, also said the US would like more information about China's intentions.
The comments come shortly after China's air force commander, Xu Qiliang, said military competition in space was a "historical inevitability".
The two countries have recently been looking to improve military ties.
Speaking to reporters, Gen Chilton said Beijing had made amazing progress in its space programme over recent years.
But he added: "Where they're heading... is one of those things that a lot of people would like to understand better."
Both countries have tried to improve military relations that were recently characterised as "on-again, off-again" by US Defence Secretary Robert Gates.
Last week Gen Chilton hosted a visit to US Strategic Command by Chinese General Xu Caihou, vice-chairman of China's Central Military Commission, the country's military decision-making body.
But while the trip was an effort to improve military ties, it is clear the two sides are also expanding their areas of competition into space.
In 2007 China surprised the world by shooting down one of its own defunct weather satellites.
And earlier this week Gen Xu Qiliang said competition in this area would continue.
"Military competition has shifted towards space. Such a shift is a major trend now, and such expansion is a historical inevitability," he told state-run media.
"To some extent, if you control space you can also control the land and the sea, and you will be in an advantageous position."