In a message broadcast on the password-protected al-Hesbah site, the group said they would also welcome a pre-election terror attack on the US because that would make a McCain win more likely.
In an endorsement that will not be welcomed by Mr McCain's flagging campaign, the group said that if al-Qaeda wants to exhaust the USmilitarily and economically, the "impetuous" Republican presidential candidate is the better choice.
"This requires presence of an impetuous American leader such as McCain, who pledged to continue the war till the last American soldier," the message said.
"Then, al-Qaeda will have to support McCain in the coming elections so that he continues the failing march of his predecessor, Bush."
Read more about McCain's newest backers by clicking here.