Raids which resulted in nine men being held last night for an alleged Birmingham-based plot to carry out an Iraqi-style kidnapping represent just the beginning of a major anti-terrorist operation, police revealed.

West Midlands Police Assistant Chief Constable David Shaw yesterday described the operation as a "very, very major investigation" which would take "days, if not weeks".

He said police were just at the "foothills" of an investigation which has already taken many months.

Mr Shaw was speaking yesterday afternoon after he revealed a ninth man had been held in connection with an alleged terrorist plot to kidnap a British Muslim soldier. Eight were arrested yesterday morning in a series of dawn raids in Birmingham, with the ninth arrested on a motorway in the city.

Security sources said the alleged plot was to abduct a serving Muslim soldier, who would have been filmed, possibly tortured and ultimately executed.

It could have mirrored the kidnappings of the British hostages Ken Bigley and Margaret Hassan by Iraqi insurgents.

Sources said a target for the alleged plot had already been identified – a young Muslim soldier in the British Army who had served in Afghanistan.

The operation to thwart the alleged plot was led by the new Midlands Counter Terrorism Unit, set up just a few months ago.

To ease community relations, police have also activated telephone advice lines in a number of languages and will distribute 5,000 leaflets offering support.

At a news conference at Lloyd House, West Midlands Police headquarters, Mr Shaw declined to give any details about the alleged plot, save to say: "I can only stress that we are right at the foothills of what is a very, very major investigation for us.

"The threat from terrorism remains very real."

He said the 4am raids marked the "culmination of many months of activity".

Sources confirmed that a surveillance operation by anti-terror officers had been in place for six months, and that there was no specific threat to the West Midlands.

The start of the news conference was delayed as officers swooped to arrest the ninth suspect on the motorway.

"That illustrates to you this is a dynamic and fluid operation that is by no means finished," Mr Shaw told reporters.

The earlier arrests were made at eight houses in the Sparkhill, Alum Rock, Kingstanding and Edgbaston areas of Birmingham. They were being searched by specialist forensic officers in black suits last night. Four commercial premises have also been secured and sealed off. Some of the nine suspects were thought to be at a high security police station in Coventry last night. Under new anti-terrorism laws, police can hold them without charge for up to 28 days.

They were arrested on suspicion of the "commission, preparation or instigation of acts of terrorism" under the Terrorism Act 2000.