"The Committee to Protect Journalists appeals for his immediate safe release," the New York-based group said in a statement.
"No purpose will be served by continuing to hold Gabriele Torsello or causing him harm," Joel Simon, the group's executive director, said in the statement.
Simon added that Torsello's kidnapping "is an indication of how much the security situation in Afghanistan has deteriorated."
Torsello, 36, is a convert to Islam who is based in London but has lived in Afghanistan for three years.
His kidnappers on Wednesday called for the withdrawal of "all Italian soldiers" from Afghanistan.
On Tuesday, they had threatened to kill the photojournalist unless another man, an Afghan convert to Christianity who has taken refuge in Italy, was returned to Kabul.
Italy granted political asylum earlier this year to Abdul Rahman, 41, who had faced a possible death penalty under Islamic Sharia law in Afghanistan for converting to Christianity.

Copyright AFP (Agence France-Presse), 2006