Russian gay rights campaigner Nikolai Alekseev is said to be applying for political asylum in Belarus.
The activist was arrested at Moscow's Domodedovo airport on Wednesday evening but apparently told his partner and a news agency he was safe in Minsk, Belarus, yesterday.
However, it appears that Mr Alekseev has only communicated by text message and supporters are questioning the validity of the messages.
In messages to Russian news agency Interfax, he reportedly said that he was withdrawing his legal challenge against Moscow authorities for banning Pride marches and would be applying for political asylum in Belarus.
The texts said he had been pressured into dropping the case, which was to be a challenge to Moscow's ruling that banning gay Pride marches is lawful.
The messages added he would still attend a protest against homophobic Moscow mayor Yuri Luzhkov next Tuesday, on the mayor's birthday.
However, some of his friends have expressed disbelief that he would abandon the court case and leave Russia for Belarus, which also has problems with homophobia.
They are also concerned that he has apparently not contacted supporters in Minsk, where he is believed to be staying, and has not phoned anyone.
Andy Harley, who runs GayNewsUK, told PinkNews.co.uk: "They [Interfax] are saying he is applying for political asylum in Belarus and withdrawing the cases in the European Court of Human Rights. This is so out of character.
"His boyfriend has only received text messages from Nikolai and he assumed they were from him. But you or I could have sent those messages. And he has not been seen or contacted by anyone in Minsk."
Mr Harley said that the campaigner's supporters feared he could be in the custody of the KGB or the FSB. He said: "The KGB in Minsk, they have a total disregard for human rights."
Another friend, New York–based journalist Doug Ireland said: “Knowing Nikolai, it is inconceivable to me that he would request political asylum in Belarus.”
It is not clear why he was arrested on Wednesday. An airport spokeswoman said he was detained because he refused to remove his shoes for a search before boarding.