Security is being stepped up at this year's Labour Party conference in the wake of last week's terrorist attacks in America.

Brighton is considered a potential terrorist target, though at the moment that threat is considered to be moderate.

Motorway-style barriers of galvanised steel will be erected around the Brighton Centre and Grand Hotel on Monday in preparation for the conference, which starts on September 30.

The barriers, which will be bolted into the road, are intended to stop potential terrorist attackers from driving vehicles into the centre or the hotel, where the conference will be based.

In the event of an emergency, the already heavily guarded site will be sealed off completely, forming a secure "island".

Security will also be high around the Metropole Hotel where many of the delegates will be staying.

As at last year's conference, the Metropole will be connected to the Grand via a footbridge so delegates can pass from one to the other without descending to street level.

There will be a high profile police presence around the island site including armed officers carrying guns.

There will be armed vehicle check points around the city centre, stopping and searching selected vehicles and people.

A five-mile air exclusion zone will exist across Brighton and Hove for the duration of the conference.

Superintendent Mark Streeter, the police officer in charge of the security arrangements for the conference, said the most likely source of a terrorist attack in Brighton was still dissident Irish republican groups such as the Real IRA and not international terrorists such as those who are thought to have carried out last week's attacks in America.

Changes in the international situation, such as military action by the US, could increase the risk.

Mr Streeter said: "The threat level is still assessed as moderate. While this has not changed we are putting into place additional measures so we can react quickly if need be.

"We want to give a very strong message that Brighton city centre and the island site are going to be an unsavoury and difficult target for potential terrorists."

Sussex Police are also launching a huge operation to control an anti-capitalist demonstration which will take place in Brighton on September 30.

As many as 5,000 people are expected to take part.

September 21 2001