WASHINGTON -- The Bush administration called it “transformational diplomacy,” an initiative that sent U.S. diplomats into war zones and other trouble spots to promote democracy and U.S. interests. But this week’s attacks on U.S. missions across the Muslim world and the killing of the U.S. ambassador and three other Americans in Libya highlight the deadly risks and high costs involved.

The effort, which has expanded under the Obama administration, has raised the personnel and financial burdens that the State Department and the Pentagon bear in protecting the more than 400 U.S. diplomatic facilities across the globe, from embassies to tiny facilities called American Presence Posts.

U.S. intelligence agencies also are under greater pressure to detect possible threats against American diplomatic facilities.

White House spokesman Jay Carney said Friday that President Barack Obama has ordered a review of all security arrangements at U.S. embassies and other diplomatic missions worldwide.

There were no specific intelligence warnings of this week’s violence, according to a U.S. intelligence official, who requested anonymity because he wasn’t authorized to speak about intelligence matters. U.S. facilities, however, were advised to be extra vigilant because Tuesday was the anniversary of the Sept. 11, 2001, terrorist attacks on the United States.

The U.S. intelligence community also sent a cable to the U.S. Embassy in Cairo alerting it to growing attention that was being paid on the Internet to a 14-minute video clip denigrating the Prophet Muhammad, the U.S. intelligence official said. The video on Tuesday ignited protests in Egypt and Yemen that by Friday expanded to two dozen countries.

The decision to put U.S. diplomatic representatives in war zones and other areas where they wouldn’t previously have been sent has been especially hard on the State Department’s Bureau of Diplomatic Security.

“The scope and the scale of our responsibilities and authorities have grown immensely in response to emerging threats and security incidents,” Assistant Secretary of State Eric Boswell, who oversees the bureau, told a Senate committee on June 29, 2011. “The department now operates diplomatic missions in places where in the past we likely would have closed the post and evacuated all personnel.”

Although its budget has risen from $300 million to around $2 billion since two 1998 al Qaida bombings of U.S. embassies in East Africa, the bureau is continuing to grapple with manpower shortages, funding constraints and other problems.

The personnel shortfall has forced the bureau to become increasingly reliant on private security contractors, who now comprise 90 percent of its workforce. They include some of the Libyan guards who were deployed outside the U.S. consulate in Benghazi when gunmen attacked on Tuesday, killing Ambassador Christopher Stevens and foreign service officer Sean Smith. Two other Americans, former Navy SEALs Tyrone Woods and Glen Doherty, were shot dead at a consular annex.

The details of the assault remain sketchy. But it appeared that Stevens had only one State Department security officer with him at the time of the attack. A pro-U.S. local militia, the 17th of February Brigade, helped drive off the assailants, U.S. officials said.

U.S. Marines, who traditionally have provided internal security at U.S. missions, are deployed at 152 embassies. But they aren’t stationed at most smaller facilities, as was the case in Benghazi, although Libya has been gripped by rising violence by militias and Islamic extremist groups that refused to disarm after last year’s ouster of the late dictator Moammar Gadhafi.