The Red Cross has called on Palestinian militant group Hamas to provide proof that captured Israeli soldier Gilad Shalit is still alive.
The aid agency made the unusual public appeal as Israel prepares to mark five years since his capture on Saturday.
The ICRC said there had been "no sign of life" from the 24-year-old in almost two years.
Hamas wants hundreds of Palestinian detainees freed from Israeli jails in exchange for the soldier.
Israeli Prime Minister Benjamin Netanyahu has rejected the demand unless some of the worst offenders - including 450 with Israeli "blood on their hands" - are exiled. Hamas has rejected this condition.
Support for a prisoner exchange deal appears to be growing among the Israeli public. A poll earlier this week showed that 63% favoured a deal, while only 19% were opposed.
Gilad Shalit was 19 when he was captured on 25 June 2006 by three armed Gaza groups, including Hamas.
He has been held ever since at a secret location in Gaza and has not been permitted visits by the Red Cross.
The last sign of life was in October 2009, when Hamas released a video of him calling on Mr Netanyahu to do everything to free him.
"The total absence of information concerning Mr Shalit is completely unacceptable," ICRC director-general Yves Daccord said in a statement.
"The Shalit family have the right under international humanitarian law to be in contact with their son," he added.