In a statement e-mailed to reporters late Tuesday, the Army of Islam threatened that British Broadcasting Corporation correspondent Alan Johnston will be "slaughtered like a sheep" if its demands are not met.
The message demanded that Abu Mohammed al-Maqdisi, who is being held in Jordan, be released. Al-Maqdisi is known as the spiritual mentor of al-Qaida leader Abu Musab al-Zarqawi.
Earlier, the group demanded freedom for Sajida al-Rishawi, an Iraqi woman sentenced to death in Jordan for her role in the al-Qaida led triple hotel bombing in Jordan in 2005 that killed 60 people, Jordan's worst terror attack. Al-Rishawi, 35, was intended to be one of the suicide bombers.
In its message, the Palestinian group also called the Hamas arrest of two of its members a "declaration of war." The group threatened to target Hamas leaders if attacked.
In response, Ghazi Hamad, spokesman for deposed Prime Minister Ismail Haniyeh of Hamas, said, "We reject the continued captivity of Alan and we are still working to release him at the soonest possible opportunity." He did not relate to the declaration of war comment.
The British Foreign Office said it was aware of the statement.
"We have made it clear that it's our top priority to see Alan Johnston released," a Foreign Office spokesman said on condition of anonymity, in line with government policy. "We condemn statements like this, which only cause further distress for his friends and family."
The British Broadcasting Corp. said in a statement, "We are aware of the reports, and are watching them closely."
Johnston was abducted from a Gaza street on March 12. His kidnapping has been condemned by governments, human rights groups, journalists' associations and Palestinian leaders.
On Monday the group posted a video message from Johnston on a militant Web site. "I have been dressed in what is an explosive belt, which the kidnappers say will be detonated if there is an attempt to storm the area," he said in the recording. "They say they are ready to turn the hideout into what they describe as a death zone if there is an attempt to free me by force."
A spokeswoman for the British Foreign Office condemned the release of the video, while Johnston's father, Graham Johnston, said his family was "most concerned and distressed at this latest development" and pleaded for Alan to be freed unharmed.