Muslim clerics condemned Abdul Rahan's release, saying it was a "betrayal of Islam" and threatened to incite violent protests.
The 41-year-old was released from the high-security Policharki prison on the outskirts of Kabul late Monday after a court dropped charges of apostasy against him because of a lack of evidence and suspected mental illness.
Justice Minister Mohammed Sarwar Danish said Rahman was staying at a "safe location" in Kabul.
Rahman has appealed to leave Afghanistan and the United Nations said it has been working to find a country willing to take him.
The Italian government said in a statement that Foreign Minister Gianfranco Fini will use a Cabinet meeting Wednesday to press for Rahman to be granted asylum there.
Fini had earlier expressed Italy's "indignation" over the case. Pope Benedict XVI also appealed to Karzai to protect Rahman.
Italy has close ties with Afghanistan, whose former king, Mohammed Zaher Shah, was allowed to live with his family in exile in Rome for 30 years. The former royals returned to Kabul after the fall of the Taliban regime in 2001.
An Italian diplomat in Kabul, who spoke on condition of anonymity because of the sensitivity of the matter, said no one from the Italian mission had been in contact with Rahman, but they had been assured his health was all right.
Rahman was arrested last month after police discovered him with a Bible during a custody dispute over his two daughters. He was put on trial last week for converting 16 years ago while he was a medical aid worker for an international Christian group helping Afghan refugees in Pakistan. He faced the death penalty under Afghanistan's Islamic laws.