Iran's foreign minister said it would be fine for a top U.S. adviser to visit Tehran, because he is of Iranian descent.
Manouchehr Mottaki said Wednesday there is no problem with Iranian-born Vali Reza Nasr visiting the country, as every Iranian has the right to do so.
Nasr is the senior adviser on Iran to the special U.S. envoy to Afghanistan and Pakistan, Richard Holbrooke.
Iranian state-run Press TV, citing other news outlets, said Nasr arrived in Tehran on an unannounced visit.
Iran has not confirmed the reports of Nasr's trip.
The reports alleged the trip is linked to Monday's release of American-Iranian journalist Roxana Saberi. The journalist was convicted of espionage and held in an Iranian jail for four months.
The Obama administration has been seeking to improve relations with Iran, and has indicated a willingness to open dialogue with Tehran on key issues including Iran's nuclear program.
Iran and the United States severed diplomatic ties nearly 30 years ago.