A top Vietnam-era military officer says he heard rumors but saw no direct evidence that nerve gas was used in the war, contradicting a report that he had confirmed the deadly chemical was used.

"I've never seen any documentation of any operation using (nerve) gas," retired Adm. Thomas Moorer said Tuesday in an interview.Instead, Moorer, who was chairman of the Joint Chiefs of Staff from 1970 to 1974, said he had simply heard unconfirmed stories that the toxic gas sarin had been used by Special Forces units, including in a 1970 operation in Laos that is under review by the Pentagon.

"Whether they (Special Forces) had sarin, you can't prove it by me either way," he said. "There were rumors that this gas had been used. But I tell everybody . . . I don't know that they used it. I don't know that they didn't use it."

A CNN-Time magazine report released over the weekend said Moorer confirmed the use of sarin gas during Operation Tailwind in Laos, in which two U.S. defectors were supposedly killed, and in other missions. The joint report also quoted several Special Forces soldiers who said they were involved in the operation, which it said had been approved by the Nixon White House and the CIA.

CNN stood by the story.