Zawahiri issued a four-minute statement in response to the September sentencing of Pakistani neuroscientist Aafia Siddiqui in a New York court.
A court sentenced Siddiqui, a former student at Brandeis University and the Massachusetts Institute of Technology, to 86 years in prison for shooting at U.S. troops. Siddiqui was convicted in February on two counts of attempted murder for trying to shoot U.S. soldiers in an Afghanistan police station two years ago.
In 2008, Siddiqui was detained near the Afghan city of Ghazni. When U.S. soldiers tried to interrogate her, she grabbed a rifle and opened fire into a crowd. She hit no one and was shot and wounded as she attempted to flee. U.S. officials said she was found with bomb-making instructions and a list of prominent New York sites, apparently a target list.
Zawahiri, in a message translated by Washington's Middle East Media Research Institute, which supplied it with United Press International, said Americans are sealing their own fate by sentencing Siddiqui.
"Imprison whomever you wish, kill whomever you wish, bomb whomever you wish, and express howsoever much pride as you can," he said, "because the Muslim Umma is behind you, bombings (will be answered) by bombings, murder (will be avenged) by murder; destruction (will bring) destruction, and hostility (will bring) hostility."
He issued similar statements directed at Pakistan, adding that anyone who wanted to see Siddiqui freed should join al-Qaida "since there is no pride and honor but through jihad."
His statements come less than a week after al-Qaida groups in Yemen were accused of targeting international freight shipments. Osama bin Laden, the top al-Qaida leader, issued warnings to French authorities last week.