Screen shots captured and published by the Post Sunday showed messages posted by the hackers -- associated with the Syrian Electronic Army -- that condemned Human Rights Watch and redirected traffic to the Syrian Electronic Army's home page.
"All Your reports are FALSE !! Stop lying!!!" one message read.
The hackers also apparently seized the HRW Twitter account, which has more than 500,000 followers.
So far, nothing indicates any sensitive information has been compromised by the hack, the Post said Sunday.
Human Rights Watch, among the world's most respected non-governmental organizations, has conducted several investigations into the human rights abuses of Assad's regime since fighting began in Syria two years ago.