Al-Qa'ida tape raises America's fears of attack on 4 July

America's terror jitters have jumped a notch with an apparently authentic warning that Osama bin Laden and most of his main al-Qa'ida lieutenants are alive and planning attacks on US targets.

The White House gave no public reaction yesterday to the audiotape message from Sulaiman Abu Ghaith, Mr bin Laden's spokesman, which was obtained by the Qatar-based Al-Jazeera television network – al-Qa'ida's main media conduit.

But senior American politicians warned that whatever the fate of Mr bin Laden himself, the threat from al-Qa'ida was real and growing, despite the military operation against it. "They are more dangerous now," said Senator John Kerry of Massachusetts, a likely Democrat challenger to President Bush in 2004.

Senator Bob Graham of Florida, head of the Senate Intelligence Committee, added that "with or without bin Laden," al-Qa'ida appeared to be regenerating. As evidence, he cited the recent attacks on Western targets in Pakistan, as well as the deadly fire in April at a synagogue in Tunisia, for which Mr Abu Ghaith claimed responsibility.

In his message, the al-Qa'ida spokesman declared that Mr bin Laden was in "good and prosperous health" and that the terror group was still capable of threatening America. "The few coming days and months will prove to the whole world, Allah willing, the truth of what we are saying."

Whatever the truth about Mr bin Laden, few doubted that Mr Abu Ghaith's message was genuine and recent. He refers to the latest Washington controversy – over Mr Bush and the intelligence services knowing enough to prevent the 11 September attacks – arguing that the row was intended to distract attention from the problems of the US economy.

He also said that "98 per cent" of al-Qa'ida's leadership, including Ayman al-Zawahiri, Mr bin Laden's Egyptian-born deputy, and the Taliban leader, Mullah Omar, had survived the US-led onslaught.

These boasts will only increase anxiety here about another al-Qa'ida attack. Hardly a day passes without another warning from the FBI, most recently that the weapon of choice might be a fuel tanker or an emergency vehicle commandeered by terrorists.

Fears are focusing on Independence Day – 4 July – when, according to a startling poll last week, a majority of Americans believe a terrorist attack will be carried out. The finding follows warnings from a string of senior administration officials that further attacks, possibly involving weapons of mass destruction, were inevitable.

Al-Qa'ida, Mr Abu Ghaith said, was now "monitoring, detecting and observing" new American targets, "which we will strike at in a period which is not long."