US hostage Kassig writes of 'stress and fear'
Abdul-Rahman Kassig, captured by Islamic State (IS) militants a year ago, says "the stress and fear are incredible" in a letter home.
His parents, who live in the US state of Indiana, have released more extracts of a letter written in captivity.
In June he wrote he was "scared to die" and saddened by the pain his ordeal was causing his family.
The aid worker was captured in Syria last year and his life was threatened in an IS video released this month.
Mr Kassig, known as Peter Kassig before he converted to Islam, wrote in the letter: "This is the hardest thing a man can go through, the stress and fear are incredible."
He said he laughed and played chess with friends but added: "I cried a lot in the first few months but a little less now. I worry a lot about you and mom and my friends.
"They tell us you have abandoned us and/or don't care but of course we know you are doing everything you can and more.
"Don't worry Dad, if I do go down, I won't go thinking anything but what I know to be true. That you and mom love me more than the moon & the stars."
On Monday, Paula and husband Ed Kassig told CBS This Morning IS militants have made unspecific demands the couple cannot meet.
They also revealed they decided to break their silence regarding their son's captivity after he was named by IS as their next victim.
Earlier this month an IS video showed the beheading of British aid worker Alan Henning and ended with a threat to Mr Kassig.
Mr Kassig's mother, Paula, has appealed via Twitter to IS leader Abu Bakr Al Baghdadi to get in touch with her.
His parents told NBC's Today show they had received an audio recording of their son two weeks ago in which he said "time was running out".
She also said her family was receiving "no help from the government", but US state department spokeswoman Jen Psaki told reporters much was being done to secure Mr Kassig's release.
"All US tools are being brought to bear," she said.
In addition to Henning, IS militants have released videos showing the beheadings of American reporter James Foley, American-Israeli journalist Steven Sotloff and British aid worker David Haines.
Another British hostage, John Cantlie, has appeared in a number of videos.
On Monday, his sister appealed for "direct contact" with the militants holding him, urging them to reopen a previous channel of communication and restart dialogue.