Police wrestled two topless women to the ground during a brief protest in St Peter's Square outside the Vatican on Tuesday after cardinals withdrew into the Sistine Chapel to begin the process of electing a new pope.
Witnesses said that at least two women took part in the protest, which followed an earlier demonstration in which women campaigners released a pink smoke flare on a hill above the Vatican.
Feminist groups have long demanded a greater role for women in the Catholic Church, which only allows men to be ordained as priests.
The identity of the women in Tuesday's protest was not immediately clear. Police officers on the scene declined to give any details.
Last month, a small group from the Ukrainian women's rights group Femen staged a similar topless protest in Milan as former prime minister Silvio Berlusconi cast his vote in Italy's general election.