Iran threatened the United States on Sunday with possible legal action for detaining five of its officials for up to 30 months in Iraq, Reuters reported.
The five Iranians were given a hero's welcome home after their release last week, waving and smiling as they stepped from their plane at Tehran's Mehrabad airport to be met by their families.
Foreign Minister Manouchehr Mottaki, who was also there to greet them, denounced their detention as "inhumane".
The capture of the Iranians, some of whom U.S. forces accused of arming Shi'ite Muslim militias at the height of Iraq's sectarian war, stoked tension between Tehran and Washington.
The two powers are also at odds over Iran's nuclear programme.
They were first handed over by their U.S. jailers to Iraq's Shi'ite Muslim-led government, which is friendly with Iran, and transferred to Iran's Baghdad embassy on Thursday. Iran says they are diplomats who were held contrary to international law.
"We reserve the right to legally pursue ... this action by the (George W.) Bush government," Mottaki said on state television, adding that they had remained detained after U.S. President Barack Obama took office in January.
One of the freed Iranians sat with his young daughter on his lap and other family members chanted "Death to America", state media reported.