The notice, sent to U.S. citizens who have signed up for the e-mail service, said the embassy had received information through the Internet about a possible attack during the week of May 10.
"We are unable at this time to determine the credibility of the threat, but we feel it is our responsibility to take all such information seriously and to share this with the American Community," the e-mail said.
"The appropriate Japanese authorities have been notified," it added.

