WASHINGTON - Effective Wednesday, force-protection levels at military bases in the continental United States are being raised in advance of the 9/11 anniversary, the Pentagon announced.

“This is not in response to any specific or credible threat surrounding the 10th anniversary of 9-11, but we believe it is prudent and precautionary to take such a step,” said DOD spokesman George Little.

Al-Qaida has shown it regards anniversaries as important dates, Little said.

“The 10th anniversary of 9/11 was mentioned in the documents seized at the Abbottabad compound” in Pakistan where al-Qaida leader Osama bin Laden was killed in May, he said.

The order remains in effect through September 11.

Both Little and spokesman Capt. John Kirby, who briefed reporters with Little on Wednesday, refused to specify the minimum force-protection level that Defense Secretary Leon Panetta has required bases to enact. Some may already be at that level or beyond, they said.

The order affects bases “mostly in the United States,” Little said.

Neither spokesman would comment on what precautions overseas bases might also be taking.

The 9/11 anniversary also prompted the U.S. State Department to issue an alert to Americans living or traveling abroad.

No specific threats have been identified, according to the alert, which added, “In the past, terrorist organizations have on occasion planned their attacks to coincide with significant dates on the calendar.”

U.S. citizens overseas who want to receive the latest travel updates and information on travel and security issues were urged to enroll in the State Department’s Smart Traveler Enrollment Program at https://travelregistration.state.gov.

Travel information is also available at http://www.travel.state.gov/. Up-to-date information on security can also be obtained by calling 1-888-407-4747 toll-free in the United States and Canada or, for callers outside the United States and Canada, a regular toll line at 1-202-501-4444.