The voice on the tape, broadcast by the Dubai-based Arabic television al-Arabiya, also told the United States that the "real battle" against it has not started yet.

"America has announced it will start putting on trial in front of military tribunals the Muslim detainees at Guantanamo and might sentence them to death," said the voice, which al-Arabiya television identified as Zawahri's.

"I swear in the name of God that the crusader America will pay a dear price for any harm it inflicts on any of the Muslim detainees."

It was the first audio tape said to be by Zawahri - considered by the US to be Osama bin Laden's right-hand man - since 2 May when another tape sent to an Arabic television also made threats against the United States.

Al-Arabiya television gave no other details about the tape.

New threats

"We tell America only one thing. What you have suffered until now is only the initial skirmishes. The real battle has not started yet," the voice said.


"I swear in the name of God that the crusader America will pay a dear price for any harm it inflicts on any of the Muslim detainees."

-Ayman al-Zawahri

"Let those who conspire with America know that America is incapable of protecting itself...and let every captive held by the infidels be assured that the day of liberation is soon," it added.

US President George W. Bush vowed last Wednesday to thwart what he said was a "real threat" of new al-Qaeda attacks and the Homeland Security Department recently warned the airline industry that al-Qaeda was planning new hijackings and bombings in the United States or abroad.

Washington blames bin Laden's al-Qaeda network for the September 11, 2001, hijacked plane attacks on the United States.

Death penalty

The United States is holding prisoner more than 600 people from 42 nations at the camp in Guantanamo Bay naval base. The prisoners include nationals from Britain, Australia, Saudi Arabia, Pakistan and Afghanistan but the US military has not given a precise breakdown.

Osama bin Laden continues to elude his US pursuers

The men, suspected members of al-Qaeda and others caught in what Bush calls the US war on terror, have been held and interrogated without being charged.

Washington said last month six foreign suspects, including two Britons and an Australian, being held at Guantanamo Bay, could face military trial as part of the war on terror.

Some of the suspects may receive the death penalty.

The United States alleges the six attended "terrorist" training camps and may have been involved in financing al Qaeda.

Bowing to pressure from Britain and Australia, the United States said later it would not seek the death penalty in any military trials held for the two British and one Australian suspects.