A new audiotape with the purported voice of Usama bin Laden (search) offers rewards of gold for the killing of U.S. and United Nations officials — from 10,000 grams for top U.S. administrator L. Paul Bremer (search) to at least 500 grams for citizens of U.N. Security Council nations.

The CIA analyzed the recording and believes it is authentic, a CIA official said on condition of anonymity.

It appeared to be the first publicized offer by bin Laden for rewards for the deaths of his enemies. He had never been known to offer rewards for missions he had described as followers' religious duty to carry out.

The 20-minute recording, dated Thursday, appeared on two Web sites known for militant Islamic messages. The voice sounded like that of bin Laden and the words were heavy with Quranic verse.

"You know that America promised big rewards for those who kill mujahedeen (holy warriors)," the speaker said. "We in Al Qaeda (search) organization will guarantee, God willing, 10,000 grams of gold to whoever kills the occupier Bremer, or the American chief commander or his deputy in Iraq."

The United States has offered rewards of its own for information leading to the captures or deaths of bin Laden and his top lieutenants, as well as for top figures in the former Iraqi government of Saddam Hussein. The price on bin Laden's head now stands at $50 million — far more than the nearly $125,000 that 10,000 grams of gold is worth.

The speaker on the tape promised a lesser prize — 1,000 grams of gold — to anyone killing a citizen of countries he called "the masters of the veto like Americans and Britons" — a reference to nations with veto power on the U.N. Security Council.

And he offered 500 grams of gold to anyone killing citizens of countries he called "slaves of the Security Council who are in Iraq, like Japan and Italy."

The context indicated the rewards applied to citizens of those countries who are in Iraq.

With gold selling Thursday on London exchanges for $387.60 a troy ounce, 10,000 grams of gold was valued at $124,630, 1,000 grams at $12,463, and 500 grams at $6,231.

Whether the tape would further fuel a wave of hostage-takings or killings of civilians in Iraq wasn't clear.

A U.S. joint congressional intelligence panel said in a report two years ago that bin Laden had agreed in 1998 to allocate $9 million in reward money for the assassination of top U.S. intelligence agency officers.

The recording promised the same 10,000-gram reward for the deaths of U.N. Secretary-General Kofi Annan and his envoy to Iraq, Lakhdar Brahimi.

"The United Nations is nothing but a Zionists' tool, even if it worked under the cover of providing humanitarian aid," the voice said. "... Whoever kills Kofi Annan or the head of his commission in Iraq or a representative like Lakhdar Brahimi, he will be awarded the same prize of 10,000 grams of gold."

It also said that if attackers died killing the targets, their families would get the reward.

The U.N. headquarters in New York said it was working with the United States to improve security.

"We're taking this (threat) seriously, and we are in consultation with the host country (the United States). We are moving to enhance the security of the secretary-general," a U.N. statement issued in New York said.

The recordings appeared on Web sites for the Ansar Islam Forum and the Islamic Research Center. Both are clearing-houses for statements by Al Qaeda and other Islamic militant groups. The forum also has a bulletin board on which extremists chat and comment on the statements.

The speaker denounced U.S. plans to hand sovereignty to Iraqis on June 30, calling them a trick to end the resistance that has killed hundreds of U.S. soldiers.

The speaker urged Iraqis to fight a holy war against their U.S.-appointed Governing Council.

He also threatened any Iraqis helping the U.S.-led coalition.

"Whoever helps the infidels against Muslims, or helps the occupying forces and whatever is affiliated to them — such as the transitional or permanent government — is committing a violation to Islam," he said, warning of consequences including "spilling blood, taking his money, separating him from his wife."