Vanessa Marzullo and Greta Ramelli were seized in July while seeking to provide healthcare assistance in the embattled northern Syrian city of Aleppo. They returned home today after being flown from Turkey.
Italian authorities have said nothing publicly about the details of negotiations to secure their release. However Italian media quoted Arab reports suggesting a ransom of $14 million may have been paid to Al Qaeda's Syrian wing, the Nusra Front.
A week after Islamist gunmen killed 17 people in Paris and a day after Belgian police killed two men during a raid on an apparently separate Islamist group, the possibility that Italian money may have gone towards financing such attacks drew an unusual level of criticism.
Maria Stella Gelmini, a senior member of the centre-right Forza Italia Party said the government should explain whether a ransom had been paid.
"I think we have to consider whether any ransom paid to terrorists could be a source of finance to bring terror into Europe," she was quoted as saying by the daily Il Sole 24 Ore.
The leader of the opposition Northern League party Matteo Salvini said on Twitter: "If the government really paid a ransom of 12 million to free the two friends of the Syrians, it would be disgusting!"
Foreign Minister Paolo Gentiloni is due to make a statement on the case to parliament later on Friday.
European governments including Italy have long tolerated or facilitated ransom payments to secure the release of hostages although the practice has frequently been denied officially.
However, the issue has become increasingly sensitive since Islamist militants beheaded a number of Western hostages, mostly American. The United States has pressed European allies not to pay ransoms.
A report in the New York Times last year said Al Qaeda and its affiliates had made at least $125 million from kidnap ransoms since 2008, most from European governments making payments through proxies.