Thousands of pieces of space junk in Earth orbit now rival weapons as a threat to the future peaceful use of space, a U.S. researcher says.

A report released by the Space Security Index, an international research consortium on space security issues, portrays space debris as a primary issue, a determination echoed by the U.S. national space policy unveiled by President Obama in June, SPACE.com reported.

Hundreds of thousands of pieces of space junk, including broken satellites, discarded rocket stages and lost astronaut tools, crowd Earth orbits. The debris could damage working spacecraft in collisions, and could be a threat on Earth if they fall back and are large enough to survive re-entering the atmosphere, the security report said.

"This is an important realization, because before that much of the security focus was on threats from hostile actors in space," Brian Weeden, a former U.S. Air Force orbital analyst, says.

"This is the first [national policy] recognition that threats can come from the space environment and non-hostile events."

The Department of Defense's U.S. Space Surveillance Network is tracking more than 21,000 objects larger than 4 inches in diameter in orbit around the Earth, officials say.