By Frank Gardner BBC Security Correspondent

The BBC's Newsnight programme has learnt that Yemen is about to launch an operation against suspected al-Qaeda members within the country.

For the United States Government it could not come too soon.

Yemen is high on its alert list of states where al-Qaeda would like to regroup.

For the past few months US special forces have been quietly training Yemeni troops to take on the terrorists.

The result is an anti-terror unit that is raring to go into action and soon will be.

I have received confidential briefings from US officials who tell me they believe some of al-Qaeda's most dangerous operatives are hiding out in the remotest parts of Yemen.

Armed escort

They tell me they are not just lying low but plotting another attack. Yemen and al-Qaeda have a known history.

Al-Qaeda attacked the warship USS Cole in Yemen

Their suicide bombers blew a hole in a billion-dollar US warship here two years ago.

US investigators have also found links between Yemenis and the 11 September plotters, and as far back as the early 1990's Osama Bin Laden is believed to have tried to blow up US troops in Aden on their way to Somalia.

Since 11 September, Yemen has taken numerous measures at Washington's request.

But tackling terror in Yemen is a highly complex task.

So I managed to persuade them to give me a visa and went to see the government, the US ambassador in his fortified embassy, and then journeyed deep into tribal territory with an escort of eight soldiers.

Army blunder

What I found has shown up how difficult it is for a country like Yemen to truly tackle terror.

The tribes may or may not be harbouring al-Qaeda but they certainly do not like any interference, either from the government or from the US.

With my armed escort I went to a desert village where a previous Yemeni army operation went disastrously wrong.

Urged on by the US, the Yemeni army surrounded the village of al-Husun and demanded it hand over two al-Qaeda suspects.

A house-to-house search had begun when an air force jet flew over and broke the sound barrier.

Thinking they were under attack, the local tribesmen opened fire on the troops, killing 18 of them.

Clearly the Yemeni Government needs better information and better co-operation from the tribes.

Dilemma

And then there is the ostrich-in-the-sand attitude from numerous government officials.

Yemeni tribal leaders are wary of outside interference

"'Al-Qaeda? What al-Qaeda? We don't have it here," is the line I was fed by officials constantly.

More worryingly for Washington, there's also a prevailing anti-American mood at street level.

With Washington perceived as Israel's staunchest supporter, most ordinary Yemenis are not keen on helping the US.

In fact they have swung the other way, often telling me they admire Osama Bin Laden as the man who stood up to George Bush.

Now, with parliamentary elections approaching next spring, there are domestic political factors to contend with.

President Ali Abdullah Saleh's party does not want to be seen as allying itself too closely to Washington for fear of losing out at the polls.

But President Saleh is caught in a dilemma.

Co-operate too closely in the War on Terror and it will cost him support at home, too little and he risks the wrath of the Pentagon's hawks.

So Yemen's leadership is treading a tightrope.

If it stumbles it may be the West that suffers the consequences.

Watch Frank Gardner's report on Newsnight at 2230 BST on BBC Two or via a live stream on this site.