The families of three American hikers held in Iran say they are growing increasingly concerned about the mental health of the trio after 16 weeks in custody.

The families of 27-year-old Shane Bauer, 31-year-old Sarah Shourd and 27-year-old Josh Fattal are asking the public to mail letters of support to the hikers.

SLIDESHOW: American Hikers Detained in Iran

Nora Shourd, the mother of Sarah Shourd, says the hikers have been treated well and seem to be physically OK, but being held in near isolation must weigh heavily on them.

The Iranian government arrested the Americans on July 31 after they strayed over the Iranian border while hiking in northern Iraq.

The families' latest statement was posted Monday on their Web site.