Tonight on Special Report with Brit Hume:

A man purporting to be Usama bin Laden's right-hand man, Ayman al-Zawahri (search), urges ongoing attacks on America and its allies in an audiotape broadcast. And Saudi Arabia joins the United States in going on high alert against terrorism.

Plus:

• Christie Whitman (search) resigns as administrator of the Environmental Protection Agency.

• U.S. soldiers guarding the American Embassy in Kabul shoot and kill four Afghan soldiers as they unload weapons destined for a nearby intelligence depot, apparently mistaking the men for assailants.

• Some 20 percent of the known radioactive materials stored at Iraq's largest nuclear facility are unaccounted for, and U.S. nuclear experts have found radioactive patches on the ground where looters dumped out barrels believed to contain hazardous materials.

• Palestinian Prime Minister Mahmoud Abbas (search) cancels a visit to this town in northern Gaza after Israeli tanks and bulldozers once again rumble in to try to destroy areas used by Palestinian militants.

Details on these stories and more on Special Report with Brit Hume.
— Guests and topics are subject to change