China is developing "counterspace" weapons that could shoot down satellites or jam signals, a Pentagon official said Friday as the United States unveiled a 10-year strategy for security in space.

"The investment China is putting into counterspace capabilities is a matter of concern to us," deputy secretary of defense for space policy Gregory Schulte told reporters as the defense and intelligence communities released their 10-year National Security Space Strategy (NSSS).

The NSSS marks a huge shift from past practice, charting a 10-year path in space to make the United States "more resilient" and able to defend its assets in a dramatically more crowded, competitive, challenging and sometimes hostile environment, Schulte said.

"Space is no longer the preserve of the US and the Soviet Union, at the time in which we could operate with impunity," Schulte said.

"There are more competitors, more countries that are launching satellites... and we increasingly have to worry about countries developing counterspace capabilities that can be used against the peaceful use of space.

"China is at the forefront of the development of those capabilities," he said.

US concerns over China's space activities have led Defense Secretary Robert Gates to seek to include space in the stability dialogue with the Chinese, Schulte said.

In 2007, China shot down one of its own weather satellites using a medium-range ground missile, sparking international concern not only about how China was "weaponizing" space, but also about debris from the satellite.

Years later, Chinese space junk is still floating around in space. Last year, debris from the satellite passed so close to the International Space Station that crew members had to change orbit and take cover.

Shooting down the satellite not only focused the world's attention on the amount of junk in space but also on Chinese counterspace capabilities, which go beyond shooting down spacecraft, said Schulte.

Among other counterspace activities, Beijing has jammed satellite signals and is developing directed energy weapons, which emit energy towards a target without firing a projectile, said Schulte.

And China isn't the only country flexing its counterspace muscle.

Iran and Ethiopia are, too, he said.

"They've jammed commercial satellites... If Ethiopia can jam a commercial satellite, you have to worry about what others can do against our military satellites.

"Fifteen years ago we didn't have to worry about that but now we have to think differently, to think about how we can continue to conduct the critical functions that are performed from space, or, if they're degraded, we have to have alternative solutions," said Schulte.

The 10-year strategy document proposes ways to protect US space assets, including by setting up international partnerships along the lines of NATO, under which an attack on one member would be an attack on all, drawing a unified response from members of the alliance.

The United States also "retains the option to respond in self-defense to attacks in space, and the response may not be in space, either," Schulte said.