As US jets bomb Taliban frontlines one of their key targets will be Osama bin Laden's ruthless "055 brigade" of Arab mercenaries.
The brigade is a small unit of highly trained, well-paid guerrilla fighters set up by Bin Laden shortly after he arrived in Afghanistan five years ago.
The highly motivated elite international group is a key target, much as Saddam Hussein's republican guard was in the 1991 Gulf war, military experts say.
The 055 brigade numbers at least 500 men. It has been based and trained at Rishikor, a former Afghan army base outside Kabul. Although it has no heavy artillery or other heavy weapons, it is believed to be equipped with sophisticated western communications equipment and night vision goggles. Military sources say it is a collection of small mobile units which has been used to back up Taliban fighters on the frontlines of the civil war.
"It is that part of al-Qaida that appears to be exclusively dedicated to the support of the Taliban," a US defence official said. It is also regarded as the most effective and disciplined foreign contingent fighting alongside the Taliban.
Motivated
The units tend to be much better motivated than regular Taliban soldiers and are used to "give backbone" to the fight and prevent defections, the official said. They "can be thrown into the front, put in various places at times of need," he added.
Early in the bombing campaign a garrison of 055 fighters near the northern city of Mazar-i-Sharif was one of the first targets for US jets. Donald Rumsfeld, the US defence secretary, described the troops as "the al-Qaida-dominated ground force".
The 055 fighters are the elite of the 3,000 Arabs who are believed to have sought sanctuary in Afghanistan. At least 1,000 more Arabs are thought to have arrived in the country since the World Trade Centre attacks, crossing over the border atpasses from Pakistan and Iran. Many are based at Jalalabad, Khost, Kandahar and Mazar-i Sharif.
"The Arabs are regarded as better fighters than the Afghans," said Kamal Matinuddin, a retired Pakistani army general. "They seem to be very loyal to Bin Laden, who is paying them well, and they are willing to die. There is every possibility that at the moment they are the main fighting elements in Taliban-controlled areas."
He said the Arab fighters were not organised along traditional army structures, and borrowed brigade names from the old Afghan army. "They have an informal set-up and their tactics are informal, too," he said.
During the 1980s war against the Soviet occupation more than 25,000 Arab volunteers, including Bin Laden, went to Afghanistan to join the mojahedin resistance. The other "Arab-Afghans", as they were known, included men from Saudi Arabia, Egypt, Algeria, Sudan, Chad, Mauritania, Somalia and Yemen, and Uyghurs from western China. Some came from Sudan, where Bin Laden set up training camps before he returned to Afghanistan, while others are said to have come from Indonesia. All were regarded as more brutal than the Afghan mojahedin.
After the war they dispersed across the world to join other insurrections, some going to the Groupe Islamique Armée in Algeria, others to fight in Kashmir, Somalia, Yemen, Azerbaijan, Bosnia, Chechnya and the Philippines.
When Bin Laden sought sanctuary in Afghanistan in 1996 other Arab-Afghans joined him. The small 055 force was set up as a foreign legion to drive ahead with the vision, shared by Bin Laden and the hardline regime, of a global Islamist revolution.
The force had close contacts with militant groups fighting against Indian security forces in Kashmir, and with Islamist organisations trying to ferment a revolt in central Asia, particularly the Islamic Movement of Uzbekistan. There were rumours in the weeks before the September 11 attacks that Juma Namangani, the movement's reclusive leader, had been appointed as one of the top commanders in the 055 brigade.
In the past three years the unit has also been used to back up Taliban attacks. One of their first reported forays inside Afghanistan was in 1998 when 055 fight ers were used in the campaign to capture Mazar-i Sharif. The troops were back in July the following year in the battle for Bamiyan. They were also believed to be behind a string of civilian massacres of the Shia population nearby in Hazarajat, including one attack early this year in which more than 200 people died.
More 055 fighters were used as part of the 20,000-strong Taliban force which took the northern city of Taloqan on September 5 last year. The loss of the city was one of the biggest setbacks to the Northern Alliance in recent years. Taloqan had been its administrative headquarters.
Since the bombing campaign began three weeks ago the 055 fighters have been moved to strategic positions around the country to prepare for a ground war with US troops.
"The British and American forces must realise that it is going to be a very long battle and it is not going to be an easy war to fight," said Dr Rohan Gunaratna, of the centre for the study of terrorism and political violence at St Andrews University.
"The ideological indoctrination is very high and this is a major factor. They can destroy a group like this, but it will be a long war.