TEHRAN - Somali kidnappers are threatening to kill Canadian journalist, Amanda Lindhout and Australian photographer, Nigel Brennan if a $2.5 million ransom is not paid in 15 days.

Tehran-based Press TV reported Monday that one of the kidnappers issued the warning to the station's correspondent in Mogadishu.

Brennan and Lindhout, a freelance television and print reporter from Sylvan Lake in central Alberta, were kidnapped on Aug 23 near Mogadishu. A Somali journalist accompanying them was also abducted.

Lindhout, 27, filed stories from Iraq on behalf of Press TV, Iran's 24-hour English-language news channel.

The National Union of Somali Journalists expressed their concern Monday over the abduction of the three journalists.

"Their long-standing detention speaks to the deterioration working conditions for journalists operating in the country" Omar Faruk Osman, the group's secretary general said in a news release posted on their website.

"We urge all who are involved the negotiations for non-political reasons to use the full extent of their influences in this matter to ensure that three colleagues are immediately and unconditionally released" Osman said.

Last month, Arab television network Al Jazeera aired footage of the kidnapped reporters surrounded by armed militants.

The group claiming to be behind the video accused Canada and Australia of "taking part in the destruction of Somalia."

Kidnappings and piracy are rife in Somalia and off its coast, emerging as a lucrative criminal racket bringing in millions of dollars in ransom.

Somali pirates are holding an arms-laden Ukrainian tanker off its coast and have said they will destroy it on Monday night or early Tuesday unless a ransom is paid.