The Pentagon understated the vulnerability faced by the nation's air and space defense command before it relocated to Colorado's Peterson Air Force Base, a newspaper reported Monday.

The North American Aerospace Defense Command moved from its longtime cave-complex home inside Cheyenne Mountain to Peterson in May. On March 3, military leaders reported to Congress that an assessment of a building at the air base that serves as the nation's homeland security nerve center found "several physical security problems."

But The Gazette of Colorado Springs said it obtained a classified document that was even more critical. According to the document, the assessment found "the existing security system at Peterson AFB ... would fail if attacked by even a low level threat."

The assessment was contained in a draft report by the Government Accountability Office as part of an ongoing GAO review of the March 3 report to Congress. That report never informed Congress whether security measures could ensure a maximum level of security at Peterson, as required.

The Peterson command center where NORAD started operating on May 28 requires a Protection Level 1, reserved for "those assets whose loss, theft, destruction, misuse or compromise would result in great harm to the strategic capability of the United States," the Gazette reported.

A final classified GAO report to Congress is due July 3. NORAD spokesman Michael Kucharek told The Associated Press the office made several classified recommendations, which have been implemented by NORAD commanders.

Kucharek added that NORAD officials will submit comments to the GAO as required.

Navy Cmdr. Gregory Hicks, a Pentagon spokesman, told the AP the military looked forward to seeing the report but that he couldn't comment on any recommendations until it's a final report.

NORAD is a binational defense agency with Canada that shares its commander with the nation's homeland security command.

Peterson Air Force Base is adjacent to Colorado Springs Airport. One security expert, Christopher Hellman of the Center for Arms Control and Nonproliferation in Washington, said he was troubled by a failure to assess the risk posed by the civilian airport's proximity.

"There's going to be lots of air traffic and that's going to make it difficult to identify whether there's hostile aircraft until the last minute, if at all," Hellman told the newspaper after being briefed on the contents of the assessment. "You won't know its intention until it's too late."

The GAO also stated that a structure at Peterson built to house the Air Force Space Command lacks "sufficient vehicle stand-off" and "a dedicated response force," the Gazette reported.

NORAD's former complex was built during the Cold War inside Cheyenne Mountain. In 2006, former NORAD-NorthCom commander Adm. Timothy Keating ordered the base moved to Peterson after problems surfaced during a joint exercise with Peterson. Keating forecast a cost savings of up to $200 million a year.

Officials decided to keep an alternate command center inside the mountain.