"We announce today the end of a phase of the Jihad (holy war) and the start of a new one... to usher in the project of an Islamic caliphate and restore Islam's glory," Abu Hamza al-Muhajer said in the message.

"We swear we will not rest from our jihad... before blowing up the filthiest house, dubbed the White House," in the course of establishing the caliphate, which began with the proclamation of an Islamic state in Iraq, he said.

The authenticity of the message could not be independently confirmed.

"The location chosen by your Mujahedeen brethren to set up their state... is but a stepping stone for the leap," Muhajer said, referring to the "Islamic state of Iraq" proclaimed last month.

Intelligence agencies have been warned that al-Qaeda may be planning to attack air and rail travel in Europe during the busy holiday travel season, CBS News reported Friday.

Citing unnamed intelligence sources, the television network said the warnings came from interrogations of al-Qaeda suspects, who recently left Afghanistan and Pakistan.

"One suspect said plans for repeating the (London) Heathrow (airport) attempt were all prepared. It is now a matter of taking action," CBS News quotes one Arab official as saying. "al-Qaeda's strategy appears to be raising the pressure in Europe."

In a move that has been puzzling intelligence agencies, al-Qaeda has been withdrawing well-trained Arab fighters from the mountains and battlefields of Afghanistan over the past six months while handing over its militant activities in Afghanistan to that country's resurgent Taliban movement, the report said.

An alliance of Sunni insurgents headed by the Iraq branch of al-Qaeda announced the creation of an independent Islamic emirate in Iraq in a video posted on the Internet on October 15, after parliament in Baghdad approved a federal constitution for the war-ravaged country.

In Friday's message, Muhajer said he had mobilized 12,000 fighters for the Islamic state and was grooming 10,000 more.

"I tell the commander of the faithful, the honourable Sheikh Abu Omar al-Baghdadi: I have put 12,000 al-Qaeda fighters at the disposal of the Islamic state of Iraq," Muhajer said, pledging allegiance to the state's emir.

The al-Qaeda chief appealed to major Iraqi Sunni insurgent groups, notably the Army of Ansar al-Sunna, the Islamic Army of Iraq and the Mujahedeen's Army, to endorse the self-styled state and pledge allegiance to its emir.

Muhajer slammed US President George W Bush, gloated over his Republican party's defeat in mid-term elections widely attributed to US involvement in Iraq, and said US forces occupying the country were preparing to cut and run.

"The enemy is now teetering under the blows of the Mujahedeen... and preparing to pack up and flee," he said.

"I thank the most stupid and worst president America -- the country of slaves and drugs -- has ever had for giving us this great historic opportunity," said the voice.

"The American people have taken the first step on the right path in order to get out of their impasse and have started to realize the treachery of their president and his subordination to Israel, voting for a measure of reason in the latest elections," Muhajer said.

"I tell (Bush): don't hurry to flee like your defence minister (Donald Rumsfeld, who resigned Wednesday). We have still not quenched our thirst for your blood."

Muhajer also charged that Bush's policies had enabled Shia Iran to spread its influence in Afghanistan, Iraq and other countries.

White House spokesman Tony Snow declined to comment on the recording.