Islamabad, Pakistan (CNN) -- Al Qaeda leader Ayman al-Zawahiri has claimed responsibility for the capture in August of a 70-year-old U.S. citizen in Pakistan, according to a number of radical websites known for carrying militants' messages.
In the eighth episode of a series called "A Message of hope and glad tidings to our people in Egypt," the speaker sent a "message of support and encouragement" to members of al Qaeda and the Taliban as well as to "our female oppressed prisoners."
"We did not forget you and we will not forget you, God willing, and therefore in order to release you, we have been successful, thanks to God almighty, to capture an American Jew called Warren Weinstein," he said.
He described the captive as "a former employee and a current contractor working with the U.S. government in its aid program to Pakistan, which aims to fight the jihad in Pakistan and Afghanistan, and just like the Americans arrest any suspect linked to al Qaeda and the Taliban, even if they were far related."
The speaker then listed eight demands that he said, if met, would result in Weinstein's release. They included the lifting of the blockade on movement of people and trade between Egypt and Gaza; an end to bombing by the United States and its allies in Pakistan, Afghanistan, Yemen, Somalia and Gaza; the release of anyone arrested on charges of belonging to al Qaeda and the Taliban; the release of all prisoners in Guantanamo and American secret prisons and the closure of Guantanamo and the other prisons; the release of terrorists convicted in the 1993 bombing of the World Trade Center; and the release of relatives of Osama bin Laden, the founder of al Qaeda who was killed in May in Pakistan.
"Your government is torturing our prisoners, and we have never tortured your prisoner," he added. "Your government signed the Geneva Conventions, and then threw it in the rubbish bin, and even though we did not sign the Geneva Conventions, we are honoring your prisoner."
The speaker said Weinstein's fate lies with U.S. President Barack Obama. "I warn you of Obama's lies and deceit because he hopes that this man gets killed so he doesn't have to worry about his problem. Obama is a liar. He lies, lies and will lie. He may say to you, 'I sought the release of your relative but al Qaeda got stubborn,' so do not believe him. And he may say to you, 'I tried to contact them, but they did not answer,' so do not believe him. He may tell you, 'I do everything in my power to release your relative,' but again do not believe him."
He urged Weinstein's relatives to pressure Obama to accede to his demands "if you want to bring back your relative."
A U.S. official said the circumstances surrounding Weinstein's disappearance have been murky, but added, "It's entirely possible that al Qaeda or one of its militant allies may be holding Mr. Weinstein and the statement by Zawahiri supports this conclusion."
The official said that, based on the materials found in the raid on Osama bin Laden's compound, al Qaeda's involvement with a kidnapping would not be surprising. "The documents from bin Laden's hideout show his frustrated deputies were considering kidnapping and other criminal enterprises as a means of striking from their weakened state," said the official, pointing to the terrorist groups' failure to conduct big attacks against Western targets.
Reached Thursday at her home in Rockville, Maryland, Weinstein's wife, Elaine, said, "I just found out myself two minutes ago when somebody told me. I have nothing to add and no information for you."
Weinstein was abducted from his home in Lahore on August 13. As his three security guards prepared for the meal before the Ramadan fast, three men knocked at the front gate and offered food for the meal -- a traditional practice among Muslims during the holy month of Ramadan, Lahore police said.
Once the gate was opened, the three men forced their way in, while five others entered the house from the back, tied up the guards and duct-taped their mouths, according to police. They pistol-whipped the driver and forced him to take them to Weinstein's room, where they hit Weinstein on the head with a pistol and forced him out of the house and into a waiting car, police said.
A police official said August 23 that three suspects had been arrested in Weinstein's kidnapping.
Weinstein works for J.E. Austin Associates Inc., a consulting firm based in Arlington, Virginia. He is a development expert, according to the company's website. The company did not immediately respond to a call and an e-mail seeking reaction.
CNN's Eric Fiegel, Pam Benson and Saad Abedine contributed to this story