The Millennium Stadium has a 72,500 capacity

Armed officers will carry out random checks on lorries coming into the city before the Manchester United and Millwall game.

They will be concentrating on vehicles carrying fuel or chemicals.

The move is in response to "heightened" terrorism fears although police stress they have received no specific threats.

Road blocks

Stephen Cahill, assistant chief constable of South Wales Police, said there would be road blocks on all of the main routes into the city from Wednesday.

"In those checks we'll be looking for vehicles that fit a certain profile," he said.

"Vehicles carrying petroleum, chemicals - large-sided vehicles that could hide something.

"And if we find that threat you've got to have the resources to deal with it, so armed officers will be in support of that operation," added the assistant chief constable.

The Millennium Stadium - which is in the heart of the city - is expected to be filled to its 72,500 capacity on Saturday.

There is no specific threat or intelligence that any incident is going to happen in south Wales this weekend Stephen Cahill

The match will also be watched by a global television audience of some 600 million in 200 countries.

In March South Wales' new chief constable Barbara Wilding warned of a risk of a terrorist attack on Cardiff, including the stadium.

Cardiff as a capital was at risk, she said, and the stadium with all its international TV exposure was a potential target for those wanting to cause maximum damage and loss of life.

"Everyone sees London as the prime target, which is totally natural, but after 9-11, we have to accept that things have changed," said Ms Wilding at the time.

"It's not just authority, the establishment and VIPs, terrorists will attack anywhere."

Her deputy Mr Cahill said on Tuesday that the police operation they were planning for this weekend had not been carried out in Cardiff before - although the risk of hooliganism from both Manchester United and Millwall fans travelling to Cardiff for the game was also being taken into consideration.

"Sadly because of incidents in Europe and worldwide over recent months, a different element, a terrorist element has come into this and we have to do it in a slightly different way.

"The dilemma is answering the disorder problem along with a perceived risk worldwide now of terrorism.

"The only thing to emphasise at this point is there is no specific threat or intelligence that any incident is going to happen in south Wales this weekend."