Palestinian militants are thought to be behind the suspected abduction of the 44-year-old, who went missing on March 12th in the Gaza Strip.
Although western journalists have previously been kidnapped in Gaza they had previously always been released within a fortnight. Mr Johnston has now been missing for 24 days.
Mr Johnston was one of the few remaining western journalists reporting on the daily lives of Palestinians living in the troubled territory. His case prompted 300 of the world's best-known journalists and reporters to call for his release in a full-page advertisement in Monday's Media Guardian newspaper.
Analysts have suggested that attempts by the Palestinian Authority to convince the kidnappers to release Mr Johnston through backwater channels may have been restricted by domestic political concerns, however.
They believe past efforts could have been inhibited by concerns that the incident could again flare up recent internecine conflict between rival Palestinian factions.
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