NEW YORK » Newly freed by the Russian authorities, Nadezhda Tolokonnikova, one of two members of the punk band Pussy Riot jailed for their political activism, had a message for the crowd at a fundraising concert in Brooklyn on Wednesday.

"We have to remember," Tolokonnikova said, "that freedom is not a given. It’s something we have to fight for."

Tolokonnikova and Maria Alyokhina, who emerged from the Russian penal system not just as outspoken critics of President Vladimir Putin of Russia, but global symbols of rebellion, were the main attractions at a benefit concert for Amnesty International at Barclays Center. Musical stars included Madonna, Blondie, Tegan and Sara, Imagine Dragons and the Flaming Lips, and the message was one of supporting human rights.

Madonna did not perform, but, in head-to-toe black, read from a long statement to welcome Tolokonnikova and Alyokhina, known to their fans as Nadya and Masha.

"It’s not a coincidence that I was on tour and that I happened to be in Moscow the day that Pussy Riot went on trial," Madonna said, because she had been horrified to hear of their 2012 arrest, on charges of hooliganism, for performing an anti-Putin song in a Moscow cathedral. She added that she had been threatened with arrest herself, for performances in Russia that were said to promote "gay behavior."

"Needless to say, I did not change one moment of my show," she said, but 87 members of her audience were arrested over displays of gay pride.

Madonna commended the punk protesters at the Barclays Center on Wednesday.

"It’s time for the rest of the world to be as brave as Pussy Riot," she said, as the women took the stage and hugged her. Alyokhina began by thanking those who had written them letters while they were in jail. "Those letters helped us stay alive," she said through an interpreter.

The women were released Dec. 23, after spending 21 months in separate remote penal colonies, their plight drawing intense international attention. Their appearance at the fundraiser Wednesday capped two whirlwind days in New York, during which they taped a slyly funny segment on "The Colbert Report," visited with the editorial board of The , met Samantha Power, the U.S. ambassador to the United Nations, and were feted by Yoko Ono and the English musician Roger Waters at a private reception for Amnesty International on the Upper East Side.

More interviews and meetings with academics and prison officials, to promote their new cause, prison reform and freedom for political prisoners, were to come, organized in part by the Voice Project, a nonprofit group that, along with Amnesty International, drummed up legal support and raised money for the women when they were jailed.

But their newfound acclaim did not sit smoothly with the other, still-anonymous members of Pussy Riot. Hours before the concert, those women emailed an open letter — translated into English — to supporters of the group.

"We are very pleased with Masha’s and Nadia’s release," they wrote. "We are proud of their resistance against harsh trials that fell to their lot, and their determination by all means to continue the struggle that they had started during their stay in the colonies."

"Unfortunately for us," the letter continued, "they are being so carried away with the problems in Russian prisons, that they completely forgot about the aspirations and ideals of our group — feminism, separatist resistance, fight against authoritarianism and personality cult, all of which, as a matter of fact, was the cause for their unjust punishment."

Tolokonnikova and Alyokhina, who have taken pains to say that they are no longer members of Pussy Riot, refused to communicate with the existing members of the group.

"Yes, we lost two friends," the letter said, "but the world has acquired two brave, interesting, controversial human rights defenders." It was signed, under assumed names, by six members of the group.

Backstage before the show, in a dressing room adjacent to Lauryn Hill’s, Tolokonnikova and Alyokhina had no comment about the letter, according to a representative, and may not have been aware of it. Onstage, they spoke mostly extemporaneously, making impassioned calls for the release of Russian political prisoners and reading from some of their legal statements. "We demand a Russia that is free," Tolokonnikova concluded, leading the crowd in an English chant: "Russia will be free!"

The audience roared. Afterward, Alyokhina and Tolokonnikova, along with Tolokonnikova’s husband, Pyotr Verzilov, were swept out of the arena quickly. They were still jet-lagged and had had an exhausting day. And besides, Madonna had invited them to dinner.

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Melena Ryzik, New York Times