Updated

On the eve of the second anniversary of the Sept. 11 terror attacks, Arabic television channel Al-Jazeera aired what it claimed is a new videotape from Usama bin Laden (search).

The satellite news channel on Wednesday broadcast footage of a man who appeared to be bin Laden hiking down a green, rocky slope shadowed by mist.

Al-Jazeera said another man seen on the tape was Ayman al-Zawahri (search), the Egyptian physician who merged his Islamic Jihad (search) organization with Al Qaeda several years ago and who is believed to be the group's day-to-day leader.

No one is heard on the video. But a speaker identified as bin Laden praises the "great damage to the enemy" on Sept. 11 and mentions five hijackers by name in an eight-minute audiotape accompanying the footage.

"Those men caused great damage to the enemy and disturbed their plans," the speaker says, praising the attackers as true believers who should become an ideal for other believers.

The news channel also broadcast a second audiotape it claimed was a recording of al-Zawahri calling on Iraqi forces to "bury" American troops in Iraq.

New video images of Al Qaeda leader bin Laden have not been seen since 2001, but there was no way to independently verify when the "new" footage was shot.

Is It Really Him?

Al-Jazeera said the videotape was made in late April or early May of this year. No snow is visible in the footage, and the grass is a bright green. A small cluster of wildflowers can be seen, suggesting -- given the apparent high altitude at which the video was shot -- that the videotape was made in early summer. At such an altitude, wild flowers would not be blooming in early September.

The videotape appeared to be shot during one day.

"This could have been made yesterday, it could have been made a year from yesterday," sources told Fox News.

Bin Laden appeared to be cooperating with the cameraman, allowing him time to move ahead in order to get a series of shots of him walking toward the camera. Bin Laden several times looks over his shoulder, giving the impression he is being followed.

Intelligence sources told Fox News that they were analyzing the tape and will compare a voice-print analysis with previous known bin Laden and al-Zawahri recordings.

Fox News commentator Mansoor Ijaz pointed out that bin Laden's beard was less gray than it was in videos released more than a year ago. He added the terrain visible on the tape appeared to be that of the northern Tribal Areas (search) of Pakistan.

American intelligence sources recently said they believed bin Laden was in about a 40-mile area along the Afghan-Pakistani border, a region out of the control of both countries' governments.

Tribes in this region would welcome bin Laden and make it their duty to protect him.

The men purported to be bin Laden and al-Zawahri are both wearing traditional Pashtun clothing and using walking sticks to hike down the rocky slope. Both men also carry what appear to be folding-stock AK-47 assault rifles.

At one point, bin Laden holds his left arm in an awkward, twisted position resting on his rifle, lending credence to the theory that he was wounded during the American-led campaign in Afghanistan. But in other shots, he removes and puts on the heavy rifle with that arm.

More Attacks Threatened

The voice attributed to al-Zawahri referred to the Sept. 11 anniversary.

"On the second anniversary of the raids on New York and Washington, we challenge America and its crusade, which is teetering from its wounds in Afghanistan and Iraq," the speaker says. "We tell them that we do not seek to kill, but we will chop off the hand which seeks to inflict harm on us, God willing."

The voice also threatens more attacks on Americans.

"What you saw until now are only the first skirmishes," the voice says. "The true epic has not begun."

The speaker refers to U.S. troops in Iraq -- an indication that it was made after American troops entered Iraq last March.

"We salute the mujahedeen brothers in Iraq and press on their hands and ask Allah to bless their sacrifices and valor in fighting the Crusaders," the speaker says. "We tell you that Allah is with you and the (Islamic) nation supports you. Depend on Allah. Devour the Americans just like the lions devour their prey. Bury them in the Iraqi graveyard."

It adds that the mothers of American soldiers should demand the U.S. government bring them home before they "return in coffins," and accused the U.S. government of hiding the true number of American casualties.

UBL Surfacing No Big Surprise

Terrorism experts and U.S. officials had expected some sort of message from Al Qaeda as the second anniversary of the Sept. 11 attacks approached.

U.S. troops in Iraq braced themselves to be on the offensive against more insurgent attacks there. Mideast press reports over the last week had suggested a new bin Laden video was set to air Wednesday, one official said.

Messages from Al Qaeda leaders are sometimes viewed as presaging an attack.

But even with Sept. 11 being Thursday, the Department of Homeland Security has no plan to raise the nation's terror alert level above yellow, its current status.

Marc Ginsburg, a Fox News foreign affairs analyst and a former U.S. ambassador to Morocco, said the tapes were a demonstration by Al Qaeda that it was still in operation, and may be a signal to sleeper cells to carry out more attacks.

But others don't seem as worried.

"Most Americans understand, I hope, that this is psychological operations," said Fox News military analyst Bill Cowan. "It's an attempt by him [bin Laden] to intimidate and scare us a little bit."

Rep. Adam Smith, D-Wash., a member of the House Armed Services Committee, said it's no surprise that bin Laden may still be alive, but "beyond that, it's really hard to say what it means in terms of Al Qaeda's organizational capacity at this point."

Bin Laden was last heard from on April 7, exhorting Muslims to rise up against Kuwait, Saudi Arabia and other governments he claimed were "agents of America." That audiotape, thought to be authentic, made a reference to the Iraq conflict, although it was not determined whether it had been recorded before the Iraq war began on March 20.

The last tape attributed to Al Qaeda was aired Aug. 18 on Al-Arabiya satellite television. The speaker, claiming to be Saudi-born militant Abdur Rahman al-Najdi, called on Muslims to travel to Iraq to fight the U.S.-led occupation.

On Aug. 3, Al-Arabiya aired an audiotape purportedly from Al-Zawahri, warning that the United States would pay dearly if it harmed detainees at Guantanamo Bay.

Bin Laden is believed to have been in the border region since December 2001, when U.S. and Afghan troops surrounded a giant cave complex in the eastern Afghan region of Tora Bora.

U.S. warplanes blanketed the area with bombs, but the Americans relied largely on local Afghan forces on the ground. Hundreds of Al Qaeda suspects are believed to have escaped across the border into Pakistan, and bin Laden may have been among them.

Fox News' Bret Baier, Paul Wagenseil and The Associated Press contributed to this report.