Three missing US nationals have been detained by Iranian guards after they crossed into Iran from Iraq, Iranian media confirmed.

The two men and a woman, described as tourists by Iraqi media, were reported to have been hiking in Iraq's Kurdish region which borders Iran.

Iranian media said the three were arrested inside Iran.

The Iraq-Iran border is generally well guarded but is not well marked in this area, correspondents say.

Iran's state-owned Al-Alam confirmed the arrests, quoting an informed source. No other details were given.