Nine people have been arrested on suspicion of terrorism-related activities in Birmingham in what has been described as a "major counter-terrorism operation".
Police carried out dawn raids in several parts of the city this morning, and 12 addresses in the Sparkhill, Washwood Heath, Kingstanding and Edgbaston areas have now been sealed off and are being searched.
Eight people were arrested this morning on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act 2000. A ninth person was picked up on a motorway near Birmingham this afternoon, and has also been arrested.
Home secretary John Reid said there was a "major investigation underway" and said he was receiving updates on the progress of the police operation.
A Home Office spokesman said the "major counter-terrorism operation" was a "reminder of the real and serious nature of the terrorist threat we face". The security threat level in Britain is currently classed as severe, which means an attack is "highly likely".
West Midlands police, which carried out the raid with the Midlands counter-terrorism unit and officers from the Metropolitan police, refused to comment on details of the suspected offences, but said the operation had required months of "meticulous planning".
Assistant chief constable David Shaw added that it was the first significant operation by the Midlands unit, one of three regional hubs set up to deal with the terrorist threat.
Recent counter-terrorism operations, notably the one in Forest Gate in east London, have been criticised for being too heavy-handed. Today Mr Shaw acknowledged the disruption caused by the operation - which could last several weeks - to the local community.
But he said his force had "exceptionally good relations" with people - many of them Muslim - in the area and said they were being kept up to date on the latest developments. About 5,000 leaflets will be distributed explaining what is happening.
A spokesman for West Midlands police added: "We are mindful that communities, locations or individuals don't become a target as a result of recent events. Hate crime will not be tolerated and we will take robust action where necessary.
"It is only with the support of all communities that terrorism can be disrupted and defeated."