June 25 (Reuters) - The family and colleagues of BBC reporter Alan Johnston, kidnapped by Islamist militants in Gaza, urged his captors on Monday not to harm him after he appeared in a video wearing what he said was an explosive belt.

Here is a short chronology of the kidnap.

March 12 - Johnston disappears while driving in Gaza.

May 9 - The "Jaysh al Islam", or Army of Islam, a little-known group, says it kidnapped him and posts a photo of his BBC identification card on the Internet.

May 17 - Johnston's 45th birthday.

June 1 - Nearly three months after the abduction, Johnston's captors release an Internet video demanding that Britain free Muslim prisoners, particularly the Islamist cleric Abu Qatada. The video shows Johnston wearing a baggy red sweater. He says he is in good health and being treated well.

June 15 - Islamic Hamas fighters take control of Gaza after a series of running battles with gunmen from the rival Fatah faction.

June 18 - Hamas says it is pressing the kidnappers to free him by the end of the day.

June 19 - It says it will try to free him by force if he is not released.

June 20 - BBC staff around the world observe a silence to mark 100 days since the abduction.

June 24 - A one-minute-long video of Johnston wearing an explosives belt is posted by the Army of Islam on a Web site used by militants. Johnston looks tired but unharmed and appeals to Hamas and the British government "not to resort to tactics of force in an effort to end this".

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