A senior US administration official, speaking on condition of anonymity, said Washington would not have approved "concessions to terrorists" which increased the risk to Nato and Afghan troops, as well as the people.
"Although we are pleased with the release of the Italian journalist, Mr Mastrogiancomo, we do have some concerns about the circumstances surrounding his release.
"It is US policy to use every appropriate resource to gain the safe return of hostages, but to make no concessions to individuals or groups holding those hostages," the official said.
Italy, which has 1,900 troops under Nato command in Afghanistan, denied in a statement that it received a formal complaint from the US through diplomatic channels.
Italy said none of the reported concerns were raised during "positive" talks between Massimo D'Alema, Italy's foreign minister, and Condoleezza Rice, the US secretary of state in Washington on Monday.
The US official said the freed Taliban were believed to include Ustad Yaser, the head of the Taliban's cultural wing, and Mofti Latifollah Hakimi, a former spokesman.
Also freed were the brother of Mullah Dadullah, a Taliban commander, and two other commanders, Hambdullah and Abdol Ghaffar.
The Taliban beheaded Mastrogiacomo's driver while his translator's whereabouts are still unknown.
An opinion poll published by La Repubblica, which employs Mastrogiacomo, showed that 51 per cent of Italians surveyed supported the swap while 41 per cent were against it.