The state-owned newspaper IRAN said the woman - identified in Farsi as Hal Talaian - had "spying equipment or a microphone" concealed in her teeth when customs authorities detained her in the border town of Nordouz, 370 miles northwest of the capital Tehran. The report said she arrived in Iran from neighboring Armenia without a visa. The paper did not say when she was detained.
But Iran's semiofficial Fars news agency quoted an unnamed official as saying the woman was taken into custody about a week ago. Fars also said she told Iranian border guards that her life would be in danger if they sent her back to Armenia.
In Washington, State Department spokesman Mark Toner said U.S. officials have yet to confirm the reports. He said the U.S. was seeking more information through Swiss officials, who represent American interests in the Islamic Republic, and the U.S. Embassy in Armenia.
"There's lots of conflicting reports swirling about on this," Toner told reporters. "What we've heard so far is precisely conflicting reports. So, frankly, rather than give those any kind of momentum or life, I'd rather just wait until we have the facts."
Armenian authorities had no immediate comment on the reported arrest.
The case, if confirmed, would be the latest point of confrontation between Iran and the United States.
In July 2009, Tehran detained three Americans - Sarah Shourd, Shane Bauer and Josh Fattal - along the Iraqi border. Initially, Tehran accused them of illegally crossing into Iran, but later added espionage charges, although authorities have given few details to support the accusations.
The U.S. has dismissed the spying charges. It says the three are innocent hikers and has repeatedly called for their release. The Americans' families have said the three were hiking in Iraq's largely peaceful mountainous northern Kurdish region and that if they crossed the border at all, they did so unwittingly.
Iranian authorities released Shourd in September on compassionate grounds on $500,000 bail. Her fiance, Bauer, and their friend Fattal remain in prison and could go on trial next month. They could face up to 10 years in prison, if convicted.
Iran has suggested in the past that the Americans in its custody could be traded for Iranians held in the U.S., raising concerns that the Americans are to be used as bargaining chips as the two countries face off over issues like Iran's disputed nuclear program.
The U.S. and its allies fear Iran's civil nuclear program is cover for the development of atomic weapons. Tehran denies the allegations, and says its nuclear program is only for peaceful purposes.
