After this morning's arrest in Manchester, Richard Beeston, Diplomatic Editor of The Times (left) explains why Syria is the main route into Iraq for foreign fighters joining the insurgency:

Foreign fighters have been known to enter Iraq from Syria, Jordan, Saudi Arabia, Kuwait and Iran. But the preferred route for militant Islamic volunteers is Syria.

Syria has a long and rugged border with Iraq. The frontier is about 300 miles long and crosses deserts, hills and mountains. It is very rugged terrain, populated by Arab tribes who have moved across the border for centuries.

Most nationals from Arab states do not require a visa to enter Syria. Once there they are recruited by supporters of the Iraqi insurgency, many of them former members of the Baathist regime, and then sent across the border.

The most popular route into Iraq seems to be down the Euphrates valley from the border town of al-Qaim, through Haditha, Hit, Ramadi, Fallujah and into Baghdad. A second supply line runs from the north through Tal Afar to Mosul.

There appears to be a loose command structure that moves the volunteers from one safe house to another, provide weapons and instructs fighters on their missions. Most of the foreign volunteers who go to Iraq seem to come from Saudi Arabia, other fighters have come from Egypt, Yemen and Syria.

There are also Muslim volunteers from Europe. French Muslims have been involved in fighting in Iraq. Last year US Marines arrested a British citizen from south London who was accused of handling weapons in Ramadi and is still under arrest.

Many of the foreigners without military experience are used as suicide bombers. Although they make up a small percentage of the insurgency they provide the rebels with the deadliest weapon in their arsenal.

The border is a huge source of tension between Syria and the coalition forces. The Iraqi government and the Americans have repeatedly accused the Syrian authorities of helping fighters cross the border.

Earlier this year, US Marines launched a series of offensives against suspected insurgent hideouts along the Euphrates Valley and have claimed some successes.

And most recently the Iraqis gave the Syrians a list of wanted people and their addresses in Damascus, but no action was taken to arrest them or halt their activities.

The Syrians are at loggerheads with America on several issues, including alleged Syrian involvement in Lebanon, continued Syrian support for militant groups like Lebanon's Hezbollah and the Palestinian extremist Hamas and Islamic Jihad.

At the same time Syria is afraid that the Bush Administration is intent on removing its regime. As a result there is a little co-operation on combatting the insurgency problem in Iraq.

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