One of two official sets of photos of Iran's famed simian space traveller depicted the wrong monkey, but a primate really did fly into space and return safely to Earth, a senior Iranian space official has said.

The two different monkeys shown in the photos released by Iran's state media caused some international observers to wonder whether the monkey had died in space or that the launch did not go well.

One set of pictures showed a relatively dark-haired monkey. Another showed a different monkey - strapped in a pod - that had light grey hair and a distinctive red mole over its right eye.

The photos stirred questions on the internet, with people joking on Facebook that the monkey "went into space and met a doctor who removed its mole," an ironic reference to some Iranians passion for cosmetic surgery.

'Archive photo'

Mohammad Ebrahimi told the The Associated Press news agency that the monkey who travelled in space was named "Pishgam," the Farsi word for pioneer.

Ebrahimi said one set of pictures showed an archive photo of one of the alternate monkeys. He said three to five monkeys are simultaneously tested for such a flight and two or three are chosen for the launch.

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Finally, the one that is best suited for the mission and is not stressed is chosen for the voyage.

State TV pictures seen by AP show the dark-haired monkey before and after the space flight, but a package of still pictures released by authorities showed the other monkey with the mole.

"I say this with certainty that the monkey is in good health and the space flight didn't have any physical effect on Pishgam," Ebrahimi said.

"Some of the photos released by one of news agencies were not related to the time of flight. They were archive photos of the monkeys being prepared for the launch."

Jonathan McDowell, a Harvard astronomer who tracks rocket launchings and space activity, also said this week's monkey space flight was real, but he had a slightly different explanation for the photo mix-up.

He claimed the light grey monkey with the mole died during a failed space mission in 2011.

"The monkey with the mole was the one launched in 2011 that died. The rocket failed. It did not get into space," McDowell said. "They just mixed that footage with the footage of the 2013 successful launch."

Iran has never confirmed that a monkey died in 2011, or that there was a failed mission that year.