LONDON, (AP) – The family of a British journalist kidnapped in the Gaza Strip pleaded Monday for his captors to “end this ordeal” following unconfirmed reports he had been killed.

The British Broadcasting Corp. said it could not confirm the claim by a previously unknown Palestinian group that said it had killed Alan Johnston, the BBC’s Gaza correspondent.

Johnston, 44, was abducted by gunmen after leaving his office in the coastal Palestinian territory on March 12. On Sunday, a previously unknown group, “The Brigades of Tawheed and Jihad,” said it had killed Johnston to support demands for the release of Palestinian prisoners held by Israel.

Palestinian officials said they could not confirm the claim. Britain’s Foreign Office said it was “urgently” investigating the reports.

In a statement, Johnston’s parents said they were going through “a desperately worrying time.”

“We make a heartfelt appeal to anybody who may have knowledge of Alan’s situation and well-being to contact the authorities in Gaza,” they said. “Our son has lived and worked amongst the people of Gaza for the last three years to bring their story to the outside world and we ask every one of them to help end this ordeal.”

More than a dozen foreign journalists and aid workers have been abducted by gunmen in Gaza in the past 18 months, often in a bid by Palestinian militants to get money or jobs. Most have been released without major physical injury within hours or days.