United States satellites could be vulnerable to attacks, according to the deputy secretary of the Defense Department, who urged the government and private sector to work together to protect the key space assets.

Deputy Secretary of Defense Bob Work, speaking during a session at the annual Space Symposium conference, said the satellites were "absolutely critical" to the operation of the US military, as well as its ability to fight future wars.

Because the session was classified, Work's comments were relayed to Reuters by his spokeswoman, Lieutenant Commander Courtney Hillson.

"We depend on space for everything from space-based communications, to intelligence, surveillance and reconnaissance to positioning, navigation and timing," Work told 200 military and industry executives, according to Hillson.

The Pentagon needs to take action to defend military and intelligence satellites, Work emphasized. That includes partnering with industry to find new ways to protect satellites and the networks used to operate them.

In addition to defense, the government needs innovative and integrated ways to respond to any such attacks to US assets in space, he said.

"To maintain our military dominance we must consider all space assets, both classified and unclassified, as part of a single constellation," Work said. "And if an adversary tries to deny us the capability, we must be able to respond in an integrated, coordinated fashion."

Work's comments at the premier space event of the year sparked concern among space warfare experts.

"His remarks seem to be part of a concerted effort by the national security establishment to 'prime the pump' so to speak for a more active counter space program for the United States," Victoria Samson, a top space analyst at the Secure World Foundation, said in an email to Breaking Defense.

"What I find interesting is the connection between classified and unclassified space programs. It seems to be elevating the unclassified programs to a point where the United States would have to treat them the same as if an attack was on a classified satellite. That would imply that things can escalate pretty quickly should we come into a time of hostility. It also means there is more room for misunderstanding, misinterpretation, or mistrust."

Last month, Admiral James Winnefeld told Reuters that the US military was taking a broader look at the overall issue of "space control," language that Theresa Hitchens said has an offensive connotation.

Hitchens, a scholar the University of Maryland's Center for International and Security Studies and former director of the United Nations Institute for Disarmament Research in Geneva, told Breaking Defense that comments by Winnefeld and Work are out of step with the national security space strategy to date under the Obama administration, which has called for strategic restraint, with an emphasis multilateral approaches to shaping the space environment.

The Pentagon is seeking an initial $5.5 billion over the next five years to beef up protection of space assets and ground networks in the wake of growing threats from China and other countries.