Despite miles of new concrete barriers, towering walls, bomb-residue tests, metal detectors, gas masks and tight restrictions on diplomats' travel, a recent tunnel found near the U.S. Embassy in Rome makes clear that America's overseas missions remain strikingly vulnerable.
They also remain a target of choice.
Since Sept. 11, officials have uncovered plots to attack U.S. embassies or consulates in Paris and Sarajevo, Bosnia, in Turkey, Lebanon and Yemen, and last week apparently in Rome.
"We're at a very high state of alert. We're taking all possible precautions," said State Department spokesman Richard Boucher.
A fresh sign of the potential risks came Saturday in Macedonia where police killed seven gunmen who were suspected of planning attacks on embassies in the capital of Skopje. A State Department official said the agency could not confirm that the U.S. Embassy was targeted.
After truck bombs simultaneously tore apart two U.S. embassies in Africa in 1998, the United States spent $4.3 billion to fortify its overseas outposts from attack.
The extra security clearly has enjoyed some successes.
At least one group considering a truck bomb attack on a U.S. Embassy in a Persian Gulf country gave up on the idea after deciding the building was too well fortified, said a U.S. official familiar with American intelligence reports, speaking on condition of anonymity.
Embassies in places including Jordan, Egypt and Saudi Arabia are ringed by high walls, concrete barriers, sophisticated cameras, armored vehicles and local guards with machine guns. Cars must go through bomb-residue tests before entering, and visitors go through metal detectors. In the last few years, some employees for the first time received gas masks and training against biological or chemical attacks.
Newer embassies are either placed far from downtowns or set back from city streets on large tracts of land.
The new embassy in Nairobi, Kenya, to replace one of the 1998 bomb targets, will be completed by early next year. Unlike the previous one, which stood close to a main downtown street, the building is in a secluded suburban area.
A temporary Nairobi embassy now in use has been set about 100 yards off a main highway, with concrete barriers 50 yards from the structure.
Critics argue that embassies remain vulnerable to things that can't be changed so easily — a location in the center of a crowded city, a connection to a city water system, a local employee's access to the building.
In addition, some worry that terrorists might target embassy families where buildings are too difficult to hit.
After the USS Cole bombing in Yemen in October 2000, some U.S. embassies in the Middle East asked American employees to keep their children home from school for a few days, fearing possible attacks. Embassies create and maintain telephone networks to spread word about threats or emergencies.
At the same time, other critics fear security has increased so much that the very purpose of diplomats overseas — to go out and gather information — is hampered.
Tim Carney, the last U.S. ambassador to Sudan, said limits on traveling to specific parts of high-risk countries "made it impossible for me to do my job sometimes."
Overseas embassies have long been targets for hostility against the United States, including the embassy in Iran, where hostages were seized in 1979.
But since the embassy bombings in Kenya and Tanzania that killed more than 250 people, attention has focused on threats from Saudi-born fugitive Usama bin Laden's Al Qaeda terror network.
U.S. officials say Al Qaeda's lack of success in carrying out attacks since Sept. 11 has resulted mostly from sweeping arrests worldwide and the war in Afghanistan.
Other security risks are hard to plug.
At most embassies abroad, local workers serve as receptionists, drivers or visa clerks and are considered crucial, particularly in places like Mexico City that process thousands of visa applications a day.
All must go through background checks and are barred from areas where classified materials are kept. They might have links, however, through relatives or religious groups, to terrorist organizations targeting U.S. missions.
One Al Qaeda suspect from Bosnia, now detained at Guantanamo Bay, Cuba, was the son-in-law of a local employee of the U.S. Embassy in Sarajevo who had keys to the building, according to officials there. The embassy shut down for several days after the man's arrest.