A purported threat toward Tokyo from a group associated with the al Qaida terror network is causing some nervousness in Japan. Officials are trying to gauge the authenticity of the threat, which promises further bombings against the United States and its allies.

An e-mail sent to a London-based Saudi newspaper (Al-Quds Al-Arabi), purportedly from an Islamic extremist named Abu Mohammed al-Ablaj, warns of car bomb attacks in Tokyo and other cities in countries allied with the United States.

The Arabic-language publication says that in the message, the group is threatening to strike Tokyo if Japan sends troops to the U.S.-led coalition in Iraq.

Prime Minister Junichiro Koizumi told reporters Monday that Japan will not give in to terrorist threats.

Chief Cabinet Secretary Yasuo Fukuda says Japan has received several security threats since the September 11, 2001 attacks in the United States and has added necessary protection.

Mr. Fukuda says the government will investigate the report and try to authenticate it. He adds that if needed, Japan will increase its vigilance, noting that it has been on guard since the September 11th attacks.

During meetings in Tokyo with U.S. Defense Secretary Donald Rumsfeld, Japanese officials said they will send troops for Iraqi reconstruction projects, but the timing depends on the security situation.

An opinion poll, released Monday by the Nippon Television network, shows 71 percent of Japanese are against sending troops to Iraq. That is up by 22 percentage points from August.

The purported threat, published in London, against Japan by the Al Qaida associate was a factor in a 3.75 percent plunge of the benchmark Nikkei index on the Tokyo Stock Exchange Monday.

Analysts say the threat also helped the U.S. dollar gain more than a full yen against the Japanese currency in Asian trading Monday.

The e-mail threat also warns of new attacks against the Australia, Britain, Israel, Italy and the United States, saying, "the cars of death will not stop at Baghdad." The message also takes credit for the twin bombings outside synagogues in Istanbul Saturday, which killed 23 people.