In an audio message released two days after the 12th anniversary of 9/11, Ayman al Zawahri said America is not a "mythic power" and that the mujahedeen - Islamic holy warriors - can defeat it with attacks on its own soil.
Al Zawahri, the successor to Osama bin Laden, used the anniversary message to argue the US could be defeated by targeting its economy. He also addressed the ongoing upheaval in the Arab world. Pointing to a power struggle going on within the rebellion against Syria's regime, he warned jihadi fighters in that country's civil war not to "compromise" with more secular or moderate rebel factions, who he said would eventually turn against the al Qaida-linked radicals.
The message could not be immediately verified but was posted on a militant website commonly used by al Qaida.
Al Zawahri, who is believed to be hiding in the Pakistan-Afghanistan border regions, said al Qaida sympathisers should stage small attacks or a "big strike" against the US, similar to the September 11 attacks in New York and Washington, leaving America in "a state of tension" about when and where the next hit would come.
He urged the Islamic world to "abandon the dollar and replace it with a currency of other countries that are not taking part in the aggression against us".
America wants to use "the Muslim people as a means to topple the pro-Iran Baathist regime and install a secular government and peaceful to Israel," al Zawahri said.
He added: "It will try to push the mujahedeen to compromise with the secular factions and the enemies of Islam."