LONDON (AP) _ Some 300 journalists called Monday for the release of British Broadcasting Corp. correspondent Alan Johnston, abducted in the Gaza Strip three weeks ago.


The appeal came in a full-page advertisement in The Guardian newspaper signed by many of Britain's best-known journalists, including veteran interviewer David Frost, host David Dimbleby and BBC presenter Jeremy Paxman, and by the editors of several national newspapers.


Johnston, 44, was kidnapped from his car by masked gunmen on March 12. He had lived in Gaza for three years, the only Western reporter permanently based in the violence-wracked Palestinian territory.


Several other Western journalists have been abducted in Gaza but none was held as long as Johnston and all were released unharmed. Many suspect that members of a powerful Gaza clan took the BBC reporter, but moves to free him have so far made little progress.


Local journalists in Gaza have held two strikes and several protests calling for Johnston to be freed.


On Monday, media watchdog the International Press Institute expressed ``grave concern'' about Johnston's fate. The Vienna-based organization's director, Johann P. Fritz, called on anyone with influence in Gaza to intensify their efforts to ensure Johnston is freed.


``His work reporting fairly and accurately from Gaza has been widely praised,'' Fritz said in a statement. ``He has shed light on one of the world's most demanding stories _ in keeping with the highest standards of the BBC.''