The kidnap and capture of journalist Alan Johnston was a "catastrophic miscalculation", London Mayor Ken Livingstone told Arab TV viewers tonight.
Livingstone said the abduction of the BBC's Gaza correspondent, who has now been missing for six weeks, had robbed the troubled territory of one of its best reporters.
He was speaking during an appeal aired on London-based TV station Al-Hiwar, calling for the 44-year-old Scot's release.
The channel broadcasts to an estimated two million people in Europe and all parts of the Arab world including Gaza, the wider Middle East and North Africa.
Livingstone said: "All the Palestinians needed was the truth to be reported, which is what Mr Johnston did. His abduction was a catastrophe.
"If you wanted to find a person whose abduction could damage the Palestinian cause, you couldn't find anyone better to do the job."
The mayor then appealed directly to Johnston's kidnappers.
He said: "Look what you have done. Instead of the foreign media continuing to report on the situation in Palestine, the media focus has been shifted to the story of the kidnapping.
"Unless the journalist is liberated it's likely that coverage of the situation will continue to be about Mr Johnston."
There has been no confirmed report on Johnston's whereabouts since he was kidnapped by masked gunmen on 12 March.
A Palestinian group last week sent a statement to news organisations claiming it had killed the correspondent.
But Palestinian President Mahmoud Abbas said that his intelligence services believed he was still alive.
Al-Hiwar presenter Anas Altikriti said Johnston went a "step further" than other reporters on Gaza by actually living in the territory.
Altikriti said: "He experienced the same conditions that they experienced on a daily basis. His abductors don't serve the best interests of the Palestinians or the people of Gaza."
Foreign secretary Margaret Beckett and the Archbishop of York, Dr John Sentamu, are among those who have called for Johnston's release.
There were renewed vigils at BBC offices today to mark his sixth week of capture.
The BBC said his sister, Katriona Johnston, joined more than 100 staff outside Broadcasting House in Glasgow with gatherings also held at BBC offices across Scotland.