Ai, who was released in June after being imprisoned for "economic crimes", tops the London-based publication's annual "power 100 list" ahead of Hans-Ulrich Obrist and Julia Peyton-Jones, curators of London's Serpentine Gallery.

Mark Rappolt, the magazine's editor, said that Ai "had reminded the art world of its wider political role, as an agent of protest outside the sometimes inward-looking domain of galleries and museums.

"His activism has been a reminder of how art can reach out to a bigger audience and connect with the real world," he added. "Institutions, while they are really important, can be great tombs."

Police accused Ai of tax evasion and the government eventually freed him due to his "good attitude" in admitting to the charges against him, his willingness to repay taxes he owes and on medical grounds. He has diabetes.

Rights groups have however said the outspoken 54-year-old, who is known for his fierce criticism of the ruling Communist Party, was detained as part of a crackdown on critics of the regime.

The artist recently covered the floor of London's Tate Modern museum with 100 million porcelain sunflower seeds as part of an exhibition and becomes only the second artist after Damien Hirst to top the ten-year-old list.

Glenn Lowry, director of New York's Museum of Modern Art, was third in the list, while Nicholas Serota, director of the Tate network of British museums, placed at sixth.