The Foreign Ministry has unofficially asked the United States to deploy armored vehicles and take other measures to tighten security around the Japanese Embassy in Baghdad following the killing of two Japanese diplomats in Iraq, government sources said Saturday.

But the U.S. has expressed reluctance, saying each nation should guard its diplomatic missions itself, the sources said. That raises a problem for Japan in terms of how to protect the embassy amid increasing fears of terrorist attacks.

Given its decision Tuesday to send Self-Defense Forces units to Iraq, Japan has begun stepping up security measures at home in response to recent warnings by the al-Qaeda terrorist network.

The ministry has also been working to tighten the embassy's current security measures, which are mainly commissioned to local security firms. Steps being considered include increasing the number of bulletproof vehicles, local security guards and escort vehicles.

Foreign Minister Yoriko Kawaguchi has recently proposed revising the SDF Law and other related legislation to enable SDF troops to guard Japan's diplomatic missions overseas, saying, "Almost all embassies in Baghdad are being guarded by their own country's military and special police forces."

But there is still caution within the government and governing coalition parties over the SDF dispatch because it may lead to the use of force abroad, which is prohibited under the Constitution.

With this in mind, the ministry asked the U.S. to upgrade its security by deploying more heavily armed U.S. troops around the Japanese Embassy. One ministry source said that so far, security measures taken by the U.S. forces "have been largely limited to patrolling" close to the embassy.