By Barnaby Mason BBC Diplomatic correspondent

Bombers in Iraq have included the Red Cross among their targets

Public information is sketchy, but the hunt has gathered momentum since this month's attack on Italian forces in southern Iraq and others on British targets in Istanbul.

The Milan public prosecutor's office issued arrest warrants for five people as part of an investigation into international terrorism.

It says the alleged ringleader arrested in Hamburg, Sheikh Mahjub Abderrazak, is a central point of reference for many extremist Islamic groups in Europe.

Italian investigators say he had contacts with some of a group of north Africans and others arrested in Italy in April - and that cell was said to belong to a Europe-wide network directed by an alleged senior figure in al-Qaeda, Abu Musab al-Zarqawi.

At that time, during the Iraq war, the cell was accused of helping militants move around Europe and of sending fighters via Turkey and Syria to training camps in north-eastern Iraq, run by the Kurdish Islamist group, Ansar al-Islam.

Sketchy intelligence

Now, the network allegedly uncovered by Italian police is said to be recruiting people to carry out suicide attacks on the American occupying forces and their allies.

Nineteen Italians were killed in a suicide attack in southern Iraq

The Italian authorities have become more worried about international terrorism since a devastating bomb attack on a police base in Nasiriya killed nineteen Italians earlier this month.

Other countries apparently singled out for attack by Osama bin Laden were Britain, Spain and Australia.

However, it is worth emphasising that the American military and senior British officials say the vast majority of attacks in Iraq are carried out by the remnants of Saddam Hussein's regime - in other words, by Iraqis rather than foreign militants.

That is not to say there are no international plots, but the sketchy information made public from time to time does not give a reliable picture of how much the authorities in Europe and elsewhere really know.