A shadowy group holding a British journalist for three months threatened on Sunday to kill him, in footage broadcast by the Al-Jazeera satellite TV channel.

A spokesman for The Army of Islam, identified as Abu Khattab, told Al-Jazeera that there was no deal to release British Broadcasting Corp. reporter Alan Johnston, and "if the situation gets more complicated concerning us and our group, then we will ingrate ourselves to Allah by slaying this journalist."

The authenticity of the video could not be independently confirmed.

In London, the BBC said it was aware of the video and was "watching developments very closely."

Responding to the video Sami Abu Zuhri, a Hamas official, said that the group was undertaking "serious and intensive efforts" to secure Johnston's release, "in spite of what was said in the tape.

"This issue is now considered a top priority. The movement is working all day and night to solve it. We will never accept any delay in ending it especially after we succeeded in resolving criminal problems in the Palestinian arena," he said.

Johnston was abducted from a Gaza City street on March 12 by a group believed to have some links to Hamas, and a message purporting to be from his captors has demanded the release of Islamic prisoners, including a cleric being held in Britain.

The deposed Palestinian prime minister, Ismail Haniyeh, said earlier on Sunday that his Hamas movement is moving in a "serious, active way" to win Johnston's release.

After taking control of the Gaza Strip last week, Hamas officials said they had made contact with Johnston's kidnappers and would work to win his release in an apparent bid to gain favour with the international community and impose order in chaotic Gaza.

The 45-year-old was seen for the first since his abduction in a video posted two weeks ago on a website used by militants.

He appeared calm and said he was being treated well and was in good health.

His disappearance is the longest of any Western journalist abducted in Gaza and has sparked numerous protests and solidarity marches in London and the Palestinian territories.