UPDATE 4:14 PM--
The Twitter account https://twitter.com/nm8smyh, which sent the original message, has been suspended. The authenticity of the account as belonging to an ISIS member has not been verified.
A reported member of the militant group Islamic State in Iraq and al-Sham (ISIS), which recently dubbed itself simply as The Islamic State, has declared that they will destroy the Kaaba in Mecca, Saudi Arabia, which is Islam's most holy site.
If Allah wills, we will kill those who worship stones in Mecca and destroy the Kaaba. People go to Mecca to touch the stones, not for Allah.
ISIS reportedly is planning to take over the city of Arar in Saudi Arabia, which is very close to the Iraq border. It is a fifteen-hour drive away from Mecca, the site of the Hajj pilgrimage which all observant Muslims are expected to do at least once.
If indeed the statement is from an ISIS member, it's a shocking one even for them, considering that ISIS has been attempting to increase recruitment from Muslims worldwide by declaring the restoration of an Islamic Caliphate.
According to John L. Esposito, Professor of Religion and International Affairs and of Islamic Studies at Georgetown University, "In terms of legitimacy- unless you're someone who's ready to join a terrorist group at this point, for the vast majority of Muslims there is no legitimacy with this group." This most recent threat reinforces Esposito's point, particularly as it comes during the holy month of Ramadan.
This piece has been updated to reflect the lack of authentication behind the reported tweet.