The mystery of an Iranian nuclear scientist who Iran says was kidnapped and tortured last year by American agents deepened Tuesday, as Iran publicized what it called a videotaped statement from him that proved its claim. That videotape was contradicted by a second videotape posted on the Internet in which a man who identified himself as the same scientist says he is studying happily in the United States.

The rival videos that claimed to show the scientist, Shahram Amiri, 32, emerged on the eve of an expected Security Council vote on a new set of American-backed economic sanctions against Iran over its nuclear program. Iran has accused the United States of extracting information about its program from Amiri.

In preparing for the vote, the Obama administration has been offering classified intelligence briefings to members of the Security Council. In these sessions, U.S. officials have used new evidence to revise previous conclusions about whether Iran has suspended efforts to design nuclear warheads, according to foreign diplomats and some American officials.

It is not clear whether information from Amiri contributed to these revised assessments.

The U.S. government has never acknowledged Amiri’s existence, much less admitted to having any role in his disappearance. But one U.S. official, declining to speak on the record about an intelligence matter, said the very fact that the video released by Iran showed someone talking over an Internet connection would suggest that he was not being held under duress.

"The United States doesn’t force people to defect or hold them here if they do," the official said. "That’s ridiculous. It’s ultimately their decision."

The official added: "Does anyone really believe that someone supposedly held captive has Internet access and the ability to make and send videos? That doesn’t make any sense."

Amiri, whom Iran has described as one of the country’s top nuclear scientists, vanished during a pilgrimage to Saudi Arabia a year ago. He worked at Iran’s Malek Ashtar University, an institution linked to the country’s powerful Revolutionary Guards.

ABC News reported March 30 that Amiri had defected to the United States, citing current and former CIA officials.

But Iranian authorities said Tuesday that the video it publicized was the first document that proved that Amiri had been abducted. The Foreign Ministry summoned the Swiss ambassador in Tehran to press a formal complaint, the ISNA student news agency reported.

The Swiss handle American interests in Tehran because Iran and the United States severed diplomatic ties after the 1979 revolution.

"In the meeting with the Swiss envoy, Iran emphasized that America is responsible for the life and well-being of Mr. Amiri," the ISNA report said. "It stressed that his abduction was against international laws and human rights."

In the Iranian video of Amiri, which was broadcast on state-run television, an announcer identified a young man, in a blurry video wearing a T-shirt and talking in Persian through a computer phone hookup, as Amiri. He said he had been kidnapped in a joint operation involving the CIA and the Saudi intelligence service in Medina on June 3, 2009. He said that he was taken to a house in Saudi Arabia, that he was injected with a shot, and that when he awoke he was on a plane heading to the United States.

He said he recorded the video on April 5 in Tucson, Ariz. The announcer said that he could not disclose how the video was obtained.

The second video, which was released shortly afterward on YouTube, showed a young man, slightly more overweight than the man in the first video, wearing a suit in a well-decorated room, who also identified himself as Amiri. He said in Farsi that he was free and safe in the United States and was working on his Ph.D. He also demanded an end to what he called faux videos about himself, saying he had no interest in politics or experience in nuclear weapons programs.

"My purpose in today’s conversation is to put an end to all the rumors that have been leveled at me over the past year," he said. "I am Iranian, and I have not taken any steps against my homeland."

The rival videos emerged as Iranian officials denied speculation that they would be willing to swap three American hikers, who have been in jail there since last summer, for Amiri.

Ramin Mehmanparast, a Foreign Ministry spokesman, said in Iranian government news accounts that it was not Iran’s practice to "exchange people whose cases are still with the judiciary," referring to the hikers who are accused of entering Iran illegally and spying.