Arabic TV station al-Jazeera has aired a videotape in which Osama Bin Laden threatens fresh attacks on the US.
Bin Laden likened the US to "corrupt" Arab governments
The leader of the al-Qaeda network says the reasons behind the events of 11 September 2001 still exist.
Americans go to the polls in four days, but Bin Laden says their security depends on neither George W Bush nor John Kerry, but on US foreign policy.
The rivals both reacted angrily to the tape, and both vowed they would stand up to the threat posed by Bin Laden.
Correspondents say that, in its simplest terms, this is a reminder from Bin Laden that he is still there and he is still a threat.
In the tape, Bin Laden speaks directly to the camera in a quiet, calm voice, making small gestures with his right hand. He appears in good health.
"Oh American people," the video begins, "my talk to you is about the best way to avoid another Manhattan; about the war, its causes and results."
He accuses President Bush of deceiving the American people in the years since the 11 September attacks.
"Bush is still deceiving you and hiding the truth from you, and therefore the reasons are still there to repeat what happened," he says.
He also accuses Mr Bush of incompetence, saying the attacks on the US would have been less severe if the president had been more alert, and suggests Mr Bush abandoned his people in a time of crisis.
He ridicules the president for continuing to read a story to schoolchildren despite having just been informed of the attacks.
The video is Bin Laden's clearest claim of responsibility yet for the attacks.
The al-Qaeda leader likens the Bush administration to Arab regimes, saying both are characterised by "hubris, arrogance, greed and unlawful acquisition of money".
He tries to appropriate the language of the Bush administration, dismissing Mr Bush's regular claims that al-Qaeda militants "hate freedom".
"We fought you because we are free and do not accept injustice," he says.
He adds: "Your security does not lie in the hands of Kerry, Bush, or al-Qaeda. Your security is in your own hands. Each and every state that does not tamper with our security will have automatically assured its own security."
Bin Laden also says he first thought of attacking the US after seeing destroyed tower blocks in Lebanon following the Israeli invasion in 1982, which he says the US permitted.
US officials say they believe the tape is authentic.
The tape alludes to Mr Bush and Mr Kerry as presidential rivals - indicating that it must have been made in the last few months.
A spokesman for al-Jazeera said the station received the tape early on Friday, but would not indicate how.
French news agency AFP quotes an unnamed US state department official as saying US diplomats in Qatar had unsuccessfully attempted to prevent al-Jazeera broadcasting the tape.
The presidential rivals both responded quickly to the tape.
Mr Bush said: "Let me make this very clear. Americans will not be intimidated or influenced by an enemy of our country. I'm sure Senator Kerry agrees with this."
The American people were at war and would prevail, he said.
Mr Kerry, meanwhile, said Americans were "absolutely united in our determination to hunt down and
destroy Osama Bin Laden and the terrorists" and he would "stop at absolutely nothing" to do so.
THE BIN LADEN TAPES
29 Oct: Al-Jazeera airs video of Bin Laden admitting he carried out 11 September attacks
15 April: Bin Laden audio tape gives Europe three months to pull troops out of Islamic nations
4 Jan: Al-Jazeera airs audio tape calling on Muslims to keep fighting holy war in Middle East
10 Sept 03: Video footage shows Bin Laden walking through rocky terrain with al-Zawahri, two taped messages accompany video
US officials have said there will be no change in the country's terrorism alert status.
Correspondents in Washington say it is difficult to predict what impact this video will have on the US presidential contest, but it is likely to dominate the rest of the campaign.
This is the first new videotape of Bin Laden speaking to have surfaced since the US-led war in Afghanistan.
However, several audio messages believed to be from him have emerged since then.
The most recent, posted on a website known to be used by Islamist militants, strongly criticised the US and coalition forces in Iraq and ordered a jihad, or holy war, against them.