A new video of kidnapped BBC journalist Alan Johnston shows him wearing an explosives vest and warning he will be blown up if Hamas continues to surround the area where he is being held, the US-based Intel Centre said in an e-mail to news organisations.
The video was released by Jaish al-Islam (Army of Islam) of Gaza, the militant group that has been holding the journalist since March, the Intel Centre said.
Only Johnston speaks on the video, which is entitled "Alan's Appeal", the Intel Centre said.
According to a transcript of Johnston's remarks, the journalist says his captors "are ready to turn the hideout into what they describe as a death zone if there's an attempt to free me by force".
Hamas has threatened to use force and storm the premise if Johnston is not freed by Monday. Hamas gunmen have surrounded the area in Gaza City's Sabra neighbourhood where the group is believed to be holding Johnston, reports in Israel have said.
Hamas is demanding the release of Johnston, 45, to prove it is able to impose law and order in the volatile coastal salient after ousting rival Fatah forces earlier this month.
"Captors tell me that very promising negotiations were ruined when the Hamas movement and the British government decided to press for a military solution to this kidnapping and the situation is now very serious," Johnston is quoted as saying. "As you can see I've been dressed in what is an explosive belt, which the kidnappers say will be detonated if there's any attempt to storm this area."
Johnston appealed to the Hamas movement and the British government not to resort to force.
"I would ask the BBC and anyone in Britain who wishes me well to support me in that appeal. It seems the answer is to return to negotiations, which I'm told are very close to achieving a deal," he said, according to the transcript released.
The BBC said it was aware of the reports of the video and was investigating.
The Scottish journalist was captured at gunpoint near his Gaza City office on March 12. He has since become the longest-held foreigner in Gaza.
On Friday, the Jerusalem Post reported that negotiations for Johnston's release had been held up because the group regards him as a life insurance against Hamas reprisals.
Mumtaz Dughmush, head of a clan involved in the kidnapping, is refusing to release the correspondent for fear that Hamas would kill him and most of his clan members, the newspaper said.
Dughmush, known as Abu Muhammad, wants assurances from Hamas that he and his relatives would not be killed, it quoted the source close to Hamas as saying.
The group, which was unknown prior to Johnston's kidnapping, has in the past demanded the release of Abu Qatada, a Palestinian-born Islamic cleric who is currently held in jail in Britain.