Detectives in Cardiff have been mounting an undercover operation targetting car thieves ahead Sunday's major soccer clash.

Arsenal play Liverpool at 1400 BST at Cardiff's Millennium Stadium in the Community Shield - the traditional curtain raiser to the football season.

When Liverpool beat Manchester United in the city last year, police saw a large rise in car crime, with 10 more cars stolen than the usual average.

Large areas of Cardiff will be closed to traffic

This year police are determined to combat theft and have mounted a specific operation against thieves.

Although renowned as a rugby venue, the Cardiff stadium has emerged as the UK's premier venue for staging football finals.

Last year's Charity Shield match - the tournament has since been renamed - passed off with few problems involving rival fans.

Two police officers were injured during scuffles involving soccer fans in the city centre on the eve of the match.

Arrested

There were also disturbances on the Saturday night before the match which were believed to have involved rival fans from Cardiff City and Manchester United fans.

A total of 15 people - the majority from Cardiff and other areas of south Wales - were arrested.

Two were arrested for assault, three for drug-related offences and 10 for public order offences.

Meanwhile, fans hoping to travel by train to Cardiff from valleys stations face frustration.

Other arrangements

Valley Lines said the line between Pontypridd and Radyr would be closed for Railtrack improvements.

Passengers have been told to make alternative arrangements.

Park-and-ride customers are advised to use Caerphilly, Lisvane, and Thornhill or Llanishen, but not Taffs Well where replacement buses are expected to be full.

Valley Lines plan to run a "more or less normal" Sunday timetable from the south of Radyr.

British Transport Police said a points failure at Bristol Parkway meant trains carrying football supporters to Cardiff were running around 25 minutes late.

Thousands of fans

Traffic congestion could hold up Sunday shoppers travelling by car unless they heed police advice.

They have been urged to avoid four junctions of the M4 as tens of thousands of football fans descend on Cardiff.

Traffic at junctions 28, 29, 32 and 33 of the motorway is expected to be particularly heavy as Liverpool and Arsenal supporters arrive for the Community Shield match.

The message from police is to avoid these junctions between 1200 and 1400 BST and after 1800 BST if at all possible.

Visiting fans will be directed to park-and-rides schemes.

Large areas of the city centre will also be cordoned off, as has become the habit ahead of the major sporting fixtures.