Osama bin Laden has urged Americans to convert to Islam in the first video message from the al-Qa'eda leader for three years, but issued no clear threat of attack as the September 11 anniversary approaches.

The newly-released video suggests that Osama bin Laden is following the news as closely as ever

The 30-minute recording contains several references to recent political events, including the appointment of Gordon Brown as prime minister and the election of Nicolas Sarkozy in France.

It is the clearest indication yet that bin Laden is still alive, despite being hunted by the US military for nearly six years with a $25 million bounty on his head.

The video shows bin Laden sitting at a table dressed in white and cream robes and wearing a white hat. Beneath him, a banner reads in English: "A message from Sheikh Osama bin Laden to the American people."

He appears tired and sallow and his beard is much shorter and darker than in his last appearance in 2004, when he sported a long beard streaked with grey.

Bin Laden addresses the American people directly, saying: "I invite you to embrace Islam" in order to achieve their "desire to stop the war" in Iraq and show "warmongering" major corporations that you have lost confidence in your democratic system".

Then, he said, "they will run after you to please you and achieve what you want to steer you away from Islam".

He said Americans elected the Democratic Party - a reference to their success in November's mid-term elections - to end the war, but they "haven't made a move worth mentioning. On the contrary, they continue to agree to the spending of tens of billions to continue the killing and war there".

The tape suggested that from his hideouts in the tribal areas of Pakistan bordering Afghanistan, he is following the news as closely as ever.

According to the transcript obtained by ABC news, bin Laden also speaks about recent issues grabbing headlines in the US, referring to "the reeling of many of you under the burden of interest-related debts, insane taxes and real estate mortgages; global warming and its woes".

He goes on to appeal to Western sentiments by criticising global warming.

"The life of all mankind is in danger because of the global warming resulting to a large degree from the emissions of the factories the major corporations.

"And despite this brazen attack on the people [referring to global warming], the leaders of the West -especially Bush, Blair, Sarkozy and Brown - still talk about freedom and human rights with a flagrant disregard for the intellects of humans?"

Al-Qa'eda has never launched an attack on the anniversary of September 11, when nearly 3,000 people were killed in the US after four planes were hijacked by terrorists.

Remaining aware of the potency of the date, it has tended to mark the date with a slew of messages rather than terrorist action.

Western intelligence agencies may take a modest amount of comfort from the fact that the tape has a more philosophical approach than previous missives and contains no specific threat of terrorism in the West, though it does promise unremitting conflict in Iraq.

It could be seen as reflecting the fact that al-Qa'eda has failed to repeat the magnitude of the September 11 attacks, and has not completed an assault on a major Western target since the July 7, 2005 bombings in London.

This summer saw failed attacks in London and Glasgow, while earlier this week German police arrested Islamic militants on the verge of attacking US interests in Europe. Rather than terrify Westerners, Bin Laden preferred to mock the US's leadership.

"Despite America being the greatest economic power and possessing the most powerful and modern military arsenal, and despite it spending on this war and its army more than the entire world spends on its armies, and being the major state influencing the world's policies as if it has a monopoly on the unjust right of veto ... 19 young men were able ... to change the direction of its compass," he said, referring to the September 11 hijackers.

Information appearing on telegraph.co.uk is the copyright of Telegraph Media Group Limited and must not be reproduced in any medium without licence.