CIA officials believe the voice on a tape released Wednesday "probably" belongs to Usama bin Laden (search), intelligence officials told Fox News.

But an official said there is no specific time reference on the tape and it could have been recorded at anytime. On Thursday, officials said they believed with a "high level of confidence" that a second voice on the tape was Ayman al-Zawahri (search), the number two person with the Al Qaeda (search) terror network.

President Bush (search) said Thursday that while the tape was still being analyzed, it "reminds us that the war on terror goes on."

"His rhetoric is trying to intimidate and create fear," Bush said after a trip to Walter Reed Army Medical Center (search), where he visited troops wounded in the war in Iraq. "He's not going to intimidate America. We are at war because of what he and his fellow killers decided to do two years ago today. We will stay the course until we have achieved our objective and dismantled the terrorist organizations."

The videotape was broadcast Wednesday over the airwaves of the Arab al-Jazeera television network. It contained a pair of voiceovers, one purportedly from bin Laden, and the other from al-Zawahri, an official said.

Initially, the technical analysis of the section with bin Laden's voice was inconclusive.

In the recording, al-Zawahri mentioned the war in Iraq, which suggested that the tape might have been recorded sometime since the fighting started in March. The voice purported to be bin Laden's speaks of some of the Sept. 11 hijackers but makes no reference to more recent events.

The Associated Press contributed to this report.