ISLAMABAD — A kidnapped 70-year-old American aid contractor is alive and in good health, being held by a Pakistani al Qaida affiliate that's likely to use him as a bargaining chip, according to militants, security officials and analysts.

Warren Weinstein, who was kidnapped in August from his home in Lahore, Pakistan, is in the custody of Lashkar-e-Jhangvi militants in North Waziristan, a ranking Pakistani militant told McClatchy. The militant said he'd seen Weinstein last month and at that point "his health was fine."

"He is being provided all available medical treatment, including regular checkups by a doctor and the medicines prescribed for him before he was plucked," the militant, who spoke only on the condition of anonymity due to the sensitivity of the issue, said last week in an interview.

Little has been revealed publicly about Weinstein's status since December, when Ayman al Zawahiri, the head of al Qaida, said in a video that the terrorist network was holding him. Weinstein, who's from Rockville, Md., had heart surgery in 2009 and suffers from high blood pressure and asthma.

Weinstein had spent several years as the Pakistan country manager for J.E. Austin Associates, a contractor for the U.S. Agency for International Development. Reportedly in ill health, he'd packed his bags and was within hours of leaving Pakistan for good on Aug. 13 when militants kidnapped him from his home in the affluent suburb of Model Town.

Mohammed Imran, a security analyst in Islamabad who maintains contact with Pakistani militant groups, said he'd received messages from militants indicating that Weinstein's captors had no plans to harm him, and that he was being provided with medical care.

"Al Qaida won't kill Weinstein. It will keep him as healthy as is possible in the circumstances, and use him as a bargaining chip in negotiations with the Pakistani authorities," he said.

Militants and security analysts said Weinstein might be traded for al Qaida members who were in Pakistani custody, or used as a human shield to prevent security forces from striking its camps in North Waziristan.

They said retired Pakistani militant commanders were acting as interlocutors to negotiate Weinstein's release, but they predicted a drawn-out process that could take years.

U.S. officials said they had no information about Weinstein's status or condition. The American government, including the FBI, is assisting in a Pakistani investigation into the kidnapping, a U.S. official based in Islamabad said.

"We remain concerned for his safety and well-being," said the official, who also spoke only on the condition of anonymity due to the issue's sensitivity. He declined to provide additional information about the case, citing privacy considerations.

A woman who answered the phone this week at Weinstein's Maryland home declined to comment. A family friend, John Bestic, said, "Because of the psychological impact to the family, the position we are taking is no comment until evidence or proof of life can be corroborated."

A daring rescue — such as the Navy SEAL operation announced Wednesday that freed two aid workers, including an American woman, who'd been held captive by Somali pirates — appeared highly unlikely in Weinstein's case. Pakistan remains furious over the U.S. raid that killed Osama bin Laden near Islamabad last May, calling it a breach of its sovereignty that badly damaged its relationship with Washington.