BBC colleagues hold vigil for Alan Johnson

A series of vigils in support of the kidnapped BBC journalist Alan Johnston have been held amid unconfirmed claims he had been killed.

His parents, politicians and colleagues called for the release of "our boy", who was abducted by masked gunmen as he returned to his apartment in Gaza City on March 12.

A previously unknown Palestinian group, The Brigades of Tawheed and Jihad, sent a statement to news organisations on Sunday claiming it had killed the Scot, who is the corporation's Gaza correspondent.

The announcement, which is being urgently investigated by British and Palestinian officials, increased the torment for Johnston's parents and colleagues, who have appealed several times for his release.

Hundreds of the 44-year-old's fellow BBC workers gathered outside the corporation's offices across the UK to show their continued support.

BBC director-general Mark Thompson addressed around 300 staff outside BBC Television Centre in London, calling for "our boy" to be allowed home.

Scores more staff gathered outside BBC offices at Birmingham and the World Service headquarters, Bush House, in London, holding posters with Johnston's picture on them.

Mr Thompson, who visited the Middle East last week to highlight the journalist's plight, said: "Alan Johnston is a modest man. "He will be surprised and perhaps even a little embarrassed by all the attention he's had in recent weeks.

"His picture is plastered all over Gaza and the West Bank and there are giant posters in London, Glasgow and Edinburgh.

"On Thursday, the UN Director-General talked about his world-wide reputation, the last in a long line of people to say nice things about him but the tributes that will mean the most to Alan Johnston are from his friends and his colleagues.

"For the past month, we have stood here to mark the moment Alan was taken five weeks ago today.

"Last Thursday, Helen Boaden (the Corporation's Director, BBC News) called him 'our boy'. "He is and we all want him home."

Colleagues from BBC offices in Scotland, where Johnston's parents live, also joined the vigils.

Johnston, who has been in Gaza for three years with the BBC, disappeared on his way home from work.

Before Sunday's statement was issued by the Brigades group, nobody had claimed responsibility for the kidnap.

The group said it killed Johnston to support demands for the release of Palestinian prisoners held by Israel.

British and Palestinian officials were today urgently trying to establish whether there was any truth behind the claim, which has not been independently verified.

Prime Minister Tony Blair's official spokesman said: "We continue to work extremely closely with the Palestinian Authority and we are urgently seeking further information from them and a number of other sources on these reports."

Senior Palestinian official Saeb Erekat added: "I urge those who abducted Johnston, instead of circulating rumours, and I hope these rumours are only rumours, is to release him immediately and without any conditions."

His parents Graham and Margaret Johnston, who live in Cairndow, Argyll, also spoke of the wish for an end to their ordeal.

They said: "This is a desperately worrying time for us.

"We make a heartfelt appeal to anyone who may have knowledge of Alan's situation and wellbeing to contact the authorities in Gaza.

"Our son has lived and worked among 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."