It is now more than four weeks since the BBC correspondent in Gaza, Alan Johnston, disappeared on his way home from work.
It is feared that he has been abducted, but there is still no clear picture of who might be holding him, where or why.
More than 6,500 people from around the world have signed a petition calling for his release.
On Monday rallies were held across the Palestinian territories and in London to call for his release.
"The longer it goes on, the more concerned that we become... what [this] must be doing to his mental state and his general health, we have no idea"
Johnston was taken hostage by masked gunmen as he returned to his apartment in Gaza City on March 12.
Kidnappers have abducted dozens of foreigners in Gaza, but none has been held so long as Johnston.
Fran Unsworth, the BBC's head of newsgathering, said: "The longer it goes on, the more concerned that we become. He is incarcerated, and what that must be doing to his mental state and his general health, we have no idea."
Lawless territory
Timeline of events
Senior members of the Palestinian government insist that they are doing all they can to locate and free the correspondent.
They have ordered security services and the interior ministry to take "all necessary measures" to secure his release.
Johnston joined the BBC World Service in 1991 and has spent eight of the last 16 years as a correspondent, including periods in Uzbekistan and Afghanistan.
He has lived and worked in Gaza for three years and was the only Western reporter permanently based in the often violent and lawless territory.
His posting in Gaza was to end at the end of March.
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