A British YouTube star was detained at a Russian-controlled space centre in Kazakhstan, the head of the Russian space agency said.
Travel blogger Benjamin Rich, who runs the Bald and Bankrupt channel, was held near one of the launch pads at the Baikonur Cosmodrome with Alina Tseliupa, Dmitry Rogozin said.
Mr Rogozin said local authorities were determining “the exact level of participation in illegal activities” by the pair.
He posted photos of Mr Rich’s visa and Ms Tseliupa’s passport.
Mr Rich specialises in travel to remote and sometimes dangerous parts of the world and has 3.5 million followers.
The blogger said he was later released by authorities and given a fine.
His most recent video was filmed in Syria and posted on 24 April.
In an Instagram post last week, he said: “Syrian suntan and back in a country with Soviet mosaics,” but did not specify where he was.
Mr Rich posted on Instagram to reveal he had been released, along with footage of him showing off buildings in the former closed Soviet city.
“I’ve woken up to a load of messages asking me if I’m OK. Apparently people think I’m in a gulag because of some Twitter post,” he said.
“Basically I was questioned by Russian police for a few hours for going to see the Buran rocket without the special permission and given a £60 administrative fine just like hundreds of foreign adventurers before me.
“The police also were nice enough to show me the closed town of Baikonur. Has an awesome mosaic of a Cosmonaut. Currently lying in my hotel room watching TC and eating Doshirak (red of course)… Hardly a gulag.”
Baikonur is now open to tourists who apply for permission from the Russian space agency Roscosmos.
It sits around 1,100km (680) miles southwest of the capital of Kazakhstan, Nur-Sultan.