The Pentagon has ordered a review of its use of social networking sites such as Twitter and Facebook, citing concerns that security could be compromised, officials said on Tuesday.

Many branches of the military use the popular, public-access sites in an effort to connect with young people, as well as to counter the propaganda of the Taliban and al Qaeda in Afghanistan and Iraq.

William Lynn, the deputy defense secretary, ordered the department-wide review in a memo to military commanders and service branch chiefs.

These tools are proving valuable in areas such as recruitment, public affairs, and quality of life for our military personnel, as well as sharing information with allies, coalition partners and military families, Lynn wrote.

However, as with any Internet-based capabilities, there are implementation challenges and operational risks that must be understood and mitigated.

Lynn asked the Pentagon's chief information officer to present a threat assessment as well as policy guidelines to ensure the responsible and effective use of emerging Internet-based capabilities to Defense Secretary Robert Gates by the end of August.

Lynn said a new policy would be developed by the end of September.

Pentagon spokesman Bryan Whitman said officials would try to strike a balance between benefits and risks arising from the use of social networking.

It does highlight the tension between recognizing these as important ways to communicate ... and yet, on the other hand, the very real security concerns that the people that maintain our networks have with respect to using these sites, he said.

NO DEPARTMENT-WIDE BAN

Whitman said the risks could be offset through a combination of technology and training.

The Pentagon has not issued a department-wide ban on the use of social networking sites, but at least some services and departments have starting clamping down.

The Marine Corps, which has long prohibited its personnel from using the sites on work computers, issued a formal ban on Monday, said Lieutenant Craig Thomas, a spokesman for the Marines.

The Marines will allow waivers for operational needs, such as for investigations, the distribution of news releases and for the recruitment of new personnel.

Marines can use the sites on their own personal computers.

Defense Secretary Robert Gates, 65, has said that he wants to utilize social networking to help the Pentagon interact with U.S. military members, many of whom are in their early 20s, and young people worldwide.

The effort has picked up pace in recent months.

When the U.S. commander in Afghanistan issued new rules for avoiding civilian casualties last month, they were published first on the Facebook page of U.S. forces in the country.

The Pentagon's Web site, www.defenselink.mil, features a link to its Facebook page and Twitter feed from its public affairs chief.

But Pentagon experts have been studying possible risks, such as whether posting to Facebook or Twitter from military computers could open a pathway for hackers.

(Additional reporting by Andrew Gray, editing by Philip Barbara)

Iraq Afghanistan Twitter