The Kurdish regional government's envoy to Washington, Qubad Talabani, told The Associated Press the three were tourists and had mistakenly crossed into Iranian territory Friday while hiking in a mountainous area near the town of Ahmed Awaa.
"The Iranians said they have arrested them because they entered their land without legal permission," he said.
Iran's state owned Arabic-language al-Alam TV station cited a "well-informed source" in the Interior Ministry that the three Americans were detained Friday after crossing into Iran's Kurdistan province.
The report said the Americans were arrested after they failed to heed warnings from Iranian border guards.
State Department spokesman Robert Wood said Friday the U.S. Embassy in Baghdad "is investigating. We are using all available means to determine the facts in this case." The U.S. Embassy said Saturday it was still unable to confirm any details.
It is relatively easy for tourists to get into the region, particularly if they arrive by airplane. The Kurdish government generally grants visitors visas valid for one week when they arrive at the airport.
A senior security official in Sulaimaniyah, near the Iranian border, said that the three were last heard from after they contacted a friend saying they had entered Iran by mistake and troops surrounded them. There has been no contact with them since, he said.
The Iranian state TV report claimed the four Americans were together when they crossed the border, but "only one returned (to Iraq), while the three were arrested."
The discrepancy could not immediately be reconciled.
According to the security official, the missing Americans were tourists hiking near Halabja and Ahmed Awaa.
The four had traveled to Turkey, then entered the Kurdish region Tuesday through the Ibrahim Al-Khalil border point in Zakho, the official said. They visited the Kurdish cities of Irbil and Sulaimaniyah on Wednesday. The next day, three of them took a taxi to Ahmed Awaa where they told their companion that they planned to stay at a nearby resort, the official said.
The mountainous border area is a popular hiking destination and well-known for its thick growth of pistachio trees.
I hope these three are soon returned home.