Two of the missiles were destined for cells operating in France, where French government security sources say terrorists planned to carry out attacks on planes at Paris’ main airport, Charles de Gaulle. The other two missiles, say intelligence sources, were to be sent to a Palestinian group operating in Lebanon.

The missiles were tracked by intelligence agencies as far as Turkey. In circumstances that are not clear, the trail was lost, and intelligence and security agencies do not know what has become of the missiles or who might have control over them.

Islamist terrorist groups have used similar missiles in the past, in part because they are easily obtained on the black market and relatively easy to operate. In June 2002, a shoulder launched missile was fired at a Saudi Air Force jet as it approached Prince Sultan Air Base in Saudi Arabia. In December of that year, another missile was fired at an Israeli charter jet as took off from the Kenyan resort of Mombasa.

Al Qaeda claimed that attack, which was timed to coincide with a suicide car bomb attack on a Mombasa beach hotel popular with Israelis. The missile misfired and didn’t hit the jet, but 10 Kenyans and three Israelis died in the hotel attack.

In 2001, a similar missile and its launcher was found near the perimeter of the airport of the Czech capital, Prague, shortly before a plane being used by then-Israeli Foreign Minister Shimon Peres was due to take off.

News that Islamist terrorist groups have once again succeeded in acquiring shoulder-launched missiles, and successfully moved them to at least the borders of Europe, comes at a time when European analysts, intelligence and security agencies and governments agree the threat of another terrorist attack is a question of when, not if.

"My assessment is that the risk is quite high, and that it is actually increasing," said French anti-terrorism Judge Jean Louis Bruguiere, adding that he believes the threat of another major terrorist attack is greater now than in the months before 9/11.

In recent weeks, as investigators in the United Kingdom continue to follow the trail of the bombers who attacked London’s transit system on July 7, senior officers of the Metropolitan police have also issued public warnings.

On the other side of the globe, Australia’s prime minister — a strong supporter of President Bush and the war in Iraq — has said that his government has "specific intelligence" of a terrorist threat. While he did not provide details, Australian media and European intelligence sources say the threat is directed against public transit in one of Australia’s major cities.

Analysts also warn that recent al Qaeda communications suggest a new focus on economic targets, and fear that an attack on financial markets in Japan could leave the global economy shaken.

"They have the capacity to shift (from fundamentalist to radical to jihadist) to convert very quickly; some of them within two weeks," he said.

Some of these Muslims are converts to Islam, many have European passports, and may belong to ethnic or national groups that have not previously attracted the attention of security agencies.

"Iraq has had, and continues to have, unfortunately, a very big impact in the promotion of jihad," said the judge. "There is even greater technical capacity because some have the capability to carry out non-conventional attacks with chemical, toxic or biological weapons."

Two years ago, an investigation launched by Bruguiere thwarted an Islamist plot linked to Abu Musab al-Zarqawi, the head of al Qaeda in Iraq, and among America’s most wanted men. The plotters, based in the Paris industrial suburb of Courneuve, had intended to use cyanide gas on targets in Paris.

Now, Bruguiere sees an even greater connection between groups operating in Europe, and an expansionist-minded al-Zarqawi. "Absolutely," he says, al-Zarqawi is trying to expand his theatre of operations beyond Iraq. "Because Iraq is considered by his group as the new land of jihad. They try from this standpoint to try and to promote and launch jihad operations outside this area, especially in Europe."

Intelligence sources tell CBS News that the shoulder-launched missiles acquired in Chechnya were destined for groups in France loyal to al-Zarqawi. Investigators have also uncovered evidence of direct communications between European cells and al-Zarqawi operatives based in or near the Middle East.

And in a shift, intelligence sources say that Iraq is no longer simply a one-way combat zone for jihadists, many of whom were used as suicide bomb fodder. Now, they say, Iraq is a training ground for operatives who will return home.

Intelligence sources told CBS News that a senior al Qaeda operative, known as Abdul Hadi al-Iraqi, was sent to Iraq at the specific request of al-Zarqawi. An assessment by a Western intelligence agency is that al-Iraqi was not needed for operations in Iraq, which have been relentless and spectacular, but that he may be used to train new terrorists who can be sent back to Europe and beyond.

Intelligence and security agencies around the world have worried about Iraq "blow-back," of confronting radicalized, highly motivated and well trained terrorists on their return to their home countries, much as the Afghan generation of jihadists who fought the Soviet occupation returned to cause problems in the Persian Gulf states, Europe and beyond.

Iraq is now such a potent tool in the hands of Islamist recruiters that experts such as Bruguiere believe the capture or killing of al-Zarqawi would have little or no impact on the threat of terrorist strikes in Europe or America.

And, possibly, only the resolution of the conflict in Iraq by political means, and the withdrawal of foreign troops, including Americans, could result in reduced threat levels and a reduction in interest in the jihadist cause.