Russia has pledged to hold a safe and secure World Cup, putting on its best face to host the world's most prestigious soccer tournament.
"We wanted to draw attention to the fact that no matter what you show foreigners, things on the inside aren't that good and pretty," 16-year-old Lika Petrovskaya told Reuters.
"No matter the pretty things that are shown, people in Russia are still suffering."
OVD-Info, a human rights organisation that monitors detentions, said that three other activists, including two minors, had been detained along with Petrovskaya outside the stadium.
The local branch of the Interior Ministry could not immediately be reached for comment.
Petrovskaya lay for a few minutes at the foot of a statue of Zabivaka, the wolf that serves as the tournament's mascot, outside the St Petersburg venue where Sweden beat Switzerland 1-0 in their round of 16 match on Tuesday.
She was not detained the first time she lay down by the statue despite the presence of security officers, and voluntarily stepped away when tourists asked her to move so they could take a picture. But she said she was detained by police when she returned for a second attempt.
Petrovskaya said one the issues she was protesting was the imprisonment of Ukrainian filmmaker Oleg Sentsov, who is being held in a Siberian jail.
Sentsov was sentenced to 20 years in a maximum security prison in 2015 after being found guilty of setting fire to two offices in Crimea, including one belonging to Russia's ruling political party, after Moscow annexed the territory from Ukraine. He was also convicted of plotting to blow up a statue.
Last month, Russian activists held a covert protest on a central Moscow street popular with World Cup fans to call on the Kremlin to release Sentsov.
(Reporting by Anton Vaganov and Gabrielle Tétrault-Farber; Editing by Mark Heinrich)
