(Adds US government has tape)

By Diala Saadeh

DUBAI, Sept 7 (Reuters) - The U.S. government was studying a copy of a purported new videotape of al Qaeda leader Osama bin Laden on Friday, which an Islamist Web site said it would soon show to mark the sixth anniversary of the Sept. 11 attacks.

U.S. officials said they were analysing the tape, which the Islamist site said was the first such bin Laden film for nearly three years, to see whether it was new or old.

The Web site, which carries messages from al Qaeda-linked groups, published a still photograph apparently from the video, which showed bin Laden looking more worn than he has in many previously available pictures.

Al Jazeera television said the tape, produced by al Qaeda's media arm al-Sahab, was likely to be shown within 72 hours.

"We can confirm that the U.S. government has the video and it is being analysed," one U.S. official said on condition of anonymity.

"We need to take a look at it to see whether it's old or new and we're doing it very quickly," a U.S. intelligence official said.

Bin Laden was last seen in a video statement on the eve of the November 2004 U.S. presidential election. Since then, he has issued several audio messages, the last in July 2006 when he vowed al Qaeda would fight the United States across the world.

His long silence has prompted two schools of thought among intelligence officials and security analysts.

Some suspected he was limiting his appearances to maximise their impact, perhaps saving his next one to coincide with a dramatic attack. Others say bin Laden, aged 50 and believed to suffer from a serious kidney ailment, may be too sick or too tightly pinned down in his hiding place to smuggle out a tape.

A year ago, a leaked French intelligence report said Saudi secret services thought bin Laden had died of typhoid in Pakistan, but Saudi Arabia said such reports were mere speculation. Michael Taarnby, specialist in militant Islamism at the Danish Institute for International Studies, said the new video would be significant as "proof of life" but would probably be more scrutinised for clues to bin Laden's health than for its message.

"I don't think we'll find any major surprises -- the usual threats, the usual diatribes against the West," he said. "Osama bin Laden is an iconic figure now but it doesn't seem he has that much control over actual events or operations."

ANNIVERSARY

White House spokesman Gordon Johndroe, accompanying President George W. Bush at an Asia-Pacific leaders' summit in Sydney, said in reaction to news of the new video:

"Six years after 9/11, the arrests in Germany and Denmark this week, and the battles we fight against al Qaeda in Iraq, Afghanistan ... remind us of the continuing threat we face from extremists and why we must continue to take the fight to them wherever they are."

Germany on Wednesday foiled a plot by Islamist militants to attack U.S. installations there and arrested three suspects believed to be members of an al Qaeda-affiliated group.

The previous day, Danish police arrested eight young Muslims on suspicion of plotting a bomb attack and having links with al Qaeda.

U.S.-led forces have been searching for bin Laden since they toppled Afghanistan's Taliban government after it refused to hand over the believed mastermind of the Sept. 11 attacks.

Bin Laden and his deputy Ayman al-Zawahri are believed to be hiding in the border area between Afghanistan and Pakistan, a mountainous, inaccessible region that U.S. intelligence has described as a safe haven for al Qaeda and the Taliban.

A video compilation showing bin Laden appeared on Islamist Web sites in July, causing much excitement in the media but the footage it shows of the al Qaeda chief was old.

The U.S. Senate voted two months ago to double the bounty on bin Laden to $50 million.

Shortly after the Sept. 11 attacks, Bush said he wanted bin Laden caught dead or alive. But the president later shifted his emphasis, saying he did not know where bin Laden was. (Additional reporting by Mark Trevelyan and Firouz Sedarat)

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