Story highlights A friend of Weinstein's said his appearance has changed dramatically

FBI says it is working to verify the authenticity of the video

Weinstein was abducted in Pakistan in August 2011

Al Qaeda has claimed responsibility and set out conditions for his release

Captured American Warren Weinstein looks tired and pale and speaks in steady monotone in pleadiang for his freedom to President Barack Obama. In a video released by al Qaeda on Christmas Day, he says he feels abandoned and forgotten since his abduction more than two years ago.

"The years have taken their toll," Weinstein, 72, says in the 13-minute video. He says he is not in good health and that he suffers from acute asthma. He appeals to Obama, Secretary of State John Kerry, the media, the American public and finally his family.

"Nine years ago, I came to Pakistan to help my government and I did so at a time when most Americans would not come here," he said. "And now, when I need my government, it seems I have been totally abandoned and forgotten."

CNN cannot independently confirm the authenticity of the video, which was first posted on The Washington Post website. It was the second apparent proof of life in which Weinstein makes a direct plea to the Obama administration. The first was released in May 2012.

"The U.S. government is working to verify the authenticity of the recently released video of Warren Weinstein," the FBI said in a statement. "We remain concerned for the safety and well-being of Mr. Weinstein and remain in contact with Warren Weinstein's family while we continue to monitor the situation."

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State Department spokeswoman Marie Harf reiterated the government's call for Weinstein to be released.

U.S. officials have repeatedly said Washington will not bargain with al Qaeda.

Weinstein was abducted August 20, 2011, from his home in Lahore, Pakistan, shortly before he was planning to return to the United States. Gunmen posing as neighbors offered food, then pistol-whipped Weinstein and his driver and tied up his guards, according to U.S. Embassy and Pakistani officials.

In the latest video, Weinstein is dressed in a light gray track suit jacket and a black cap. He looks very different from when he was captured; he is gaunt and has a salt-and-pepper beard.

"Needless to say, I've been suffering deep anxiety every part of every day, not knowing what is happening to my family and not knowing how they are and because I am not with them," Weinstein said.

His appearance alarmed Laurie Wiseberg, who is a friend and former colleague of Weinstein.

"Quite honestly, I didn't recognize him in the picture. He has changed so dramatically from the person he used to be in terms of appearance and I would hope something could be done so he has a chance to be reunited with his family, his wife, his children and grandchildren, and not have to die in a foreign country far away from those he loves," Wiseberg told CNN's Don Lemon.

Wiseberg said she last spoke to Weinstein's wife "some months ago and she was quite in despair, but hoping very much that he would in fact be released."

In the video, Weinstein said his captors have agreed to let his family visit him, but only if Obama agrees to do the same for al Qaeda members held by the United States.

"Unless you continue to try to get President Obama and his administration to actively pursue my release, we may never see each other again," he said.

Weinstein was employed by J.E. Austin Associates Inc., a U.S. consulting firm based in Arlington, Virginia, that is a USAID contractor. He is a world-renowned development expert, according to the company's website.

No one else appears in the latest video of Weinstein. In it, he appeals to Obama as a family man.

"I am, therefore, appealing to you, on a humanitarian basis, if nothing else, in asking that you take the necessary actions to expedite my release and my return to my family and to my country. Our country."

Toward the end, he focuses on his wife and family.

"I would like them to know I love them very much and I think about each and every one of them every moment of every day of my captivity."

Weinstein's wife, Elaine, who lives in Rockville, Maryland, was not immediately available for comment.