Madonna said she will be "honoured" to introduce two members of the campaigning Russian punk band Pussy Riot on stage at an Amnesty International concert next month.
The chart star will join Maria Alyokhina and Nadezhda Tolokonnikova at the campaign group's Bringing Human Rights Home concert.
They were recently released after nearly two years in jail following a conviction for hooliganism when they staged a protest in a Russian church.
The pair will address music fans at the concert in New York, which also features The Flaming Lips and Lauryn Hill in the line-up, on February 5.
Comparing herself to the pair, Madonna said: "I am honoured to introduce my fellow freedom fighters Masha and Nadya from Pussy Riot.
"I have admired their courage and have long supported their commitment and the sacrifices they have made in the name of freedom of expression and human rights."