The family and colleagues of Alan Johnston, a BBC reporter kidnapped by Islamists in Gaza, urged his captors yesterday not to harm him after he appeared in a video wearing what he said was an explosives belt.

Johnston's father said he and his family were "most concerned and distressed" about the video, in which the 45-year-old Briton said his kidnappers had threatened to blow up the belt of explosives if force was used to free him.

The BBC also said it was "very distressing" to see Johnston "being threatened in this way".

"Our thoughts, of course, are with Alan in his present predicament. We earnestly request his abductors to release Alan unharmed in any way," Johnston's father said in a statement.

In the one-minute-long video posted by the Army of Islam on a website used by militants, Johnston looked tired but unharmed and appealed to the Hamas movement and the British government "not to resort to tactics of force in an effort to end this".

Hamas spokesman Fawzi Barhoum said in Gaza, where the movement took control in a civil war more than a week ago, that contacts were under way with Johnston's captors to gain his release through peaceful means.

"We will work in every way to free Alan Johnston without putting his life at risk," Barhoum said. "Preserving Alan's life and freedom is better than shedding blood and maybe that will cost us more time."

Johnston appeared in the video wearing a white and blue belt around his torso with black shoulder straps over a dark red sweater in the undated video filmed against a black background.

Johnston's captors say they want Britain to free Muslim prisoners, particularly Islamist cleric Abu Qatada, in exchange for the reporter's release.

Hamas officials in the Gaza Strip say they are pressing the kidnappers to free Johnston, but Ismail Haniyeh, the prime minister of the Hamas-led government sacked by Palestinian President Mahmoud Abbas of Fatah, said on Sunday his group had not used force to try to free Johnston at the request of the British government, fearing he might be harmed in the process.

"We ask those holding Alan to avoid him being harmed by releasing him immediately," the BBC said in a statement.

Johnston was abducted in Gaza on March 12 and is believed to be being held by the Army of Islam.