Computer hackers say they breached the Central Intelligence Agency's website late Wednesday.
The CIA's public website experienced problems throughout the evening, and a group of hackers who call themselves "Lulz Security" said in a Twitter message: "Tango down - cia.gov."
"Lulz Security" only claimed that it attacked the CIA's website. There was no immediate indication that sensitive data in the agency's internal computer network was accessed.
A CIA spokeswoman said the agency is looking into the report.
The same group of hackers has claimed responsibility for recent attacks on websites operated by the U.S. Senate, Sony Corporation, Nintendo and the Public Broadcasting System television network in the United States.
The group is believed to have members in other countries as well as the United States. It has suggested its exploitation of public websites is intended to highlight weaknesses in cybersecurity.
Some information for this report was provided by AP, AFP and Reuters.