UN Secretary-General Ban Ki-moon on Thursday called for the unconditional and immediate release of the British Broadcasting Corporation (BBC)'s correspondent Alan Johnston who was abducted by unknown gunmen in Gaza a month ago.

Ban said in a statement that he has been closely following the abduction of the BBC journalist.

"I am deeply concerned. Even after one month of his abduction, he has not been released," he said.

Noting that Johnston's coverage of Palestinian issues has earned a great reputation worldwide, Ban said freedom of coverage, as well as freedom of the press, should be protected as a matter of principle.

"I sincerely hope that those who are responsible for this abduction should release him unconditionally and immediately. I will do whatever I can in my capacity as secretary-general," he said.

On March 12, Johnston, who has been working in Gaza as a reporter for BBC since 2004, was stopped by unknown masked gunmen while he was driving his car and abducted at a gunpoint.