Tributes are pouring in for six Sussex-trained soldiers killed during a gunfight in Iraq.

Prime Minister Tony Blair said the troops, who had been helping Iraqis form their own police force, had been doing an extraordinary and heroic job.

It has emerged the soldiers, all members of the Royal Military Police (RMP), known as Redcaps, were shot dead during a day of violence in the southern town of Al Majar Al-Kabir, 100-miles north of Basra.

The Redcaps had been trained at the Roussillon Barracks in Chichester and would have returned to the city for further courses.

Their deaths have thrown the city into mourning at a time when many military personnel were preparing to celebrate the 200th anniversary of the barracks with a march through Chichester tomorrow by 100 soldiers.

The Army says the march will still go ahead with a thanksgiving service held in Chichester Cathedral.

Soldiers will be joined by 100 veterans and members of affiliated associations including Chelsea Pensioners for the service, which is being taken by the Dean, the Very Reverend Nicholas Frayling.

Among the VIPs attending will be Hugh Wyatt, the Lord Lieutenant of West Sussex, and the Duke of Richmond and Gordon.

After the service there will be a lunch at the barracks, followed by a party for people living near the headquarters in the evening.

The Redcaps form one of the smallest corps in the Army, with just over 2,000 members.

They have been in Chichester since 1964, occupying barracks built by French prisoners during the Napoleonic War and named after a great British victory.

The barracks was previously home to the Royal Sussex Regiment, now part of the Princess of Wales' Royal Regiment.

Last night, flags flew at half-mast as residents in Chichester paid their respects and laid flowers at the barracks.

Well-wishers signed a book of condolence at the base's museum and approached guards with messages of support.

Chichester City Council was flying the Union flag at half-mast outside its chambers in North Street and other municipal buildings.

Meanwhile, the Bishop of Chichester, the Right Reverend John Hind, said: "The very first thing I want to do is express my deepest sympathy to the families, colleagues and friends of those who were killed.

"As far as Chichester and the Roussillon Barracks are concerned, it is particularly tragic this should have happened just a few days before the celebrations for the 200th anniversary of the presence of the barracks here.

"When I was Bishop in Europe I saw something at first hand of the way which British soldiers, and especially members of the RMP, go about the costly business of peace keeping and civil reconstruction in the immediate aftermath of the Kosovo war.

"It wasn't just the way they tried to create confidence in as non-threatening way as possible, but also the relationships they quickly struck up with local people and especially children.

"What it all shows however is that peace and justice don't come without a cost and it is right to pay tribute to the six members of the RMP who are part of the price being paid for the reconstruction of Iraq.

"That is cold comfort for those who are grieving at the moment, but I hope it may be some consolation to them in the long run."

Andrew Tyrie, MP for Chichester, said: "My thoughts are with the families and those who have been affected in the local community by this.

"The Royal Military Police are very much part of the local community in Chichester."

City mayor, Councillor Jean Le Bourlier-Woods,said: "It has come as a big shock. All one can say is the people of Chichester send their regrets to the barracks and the families of the soldiers concerned.

"It is a very sad day for us. It brings home the horrors of war."

Captain Philip Packer, adjutant at the Chichester barracks, said: "We are all deeply saddened by the tragic news of the loss of colleagues and our thoughts are with family and friends.

"Tomorrow's parade is an event we are sharing with our community in Chichester and West Sussex and it will be an occasion when we will remember all our comrades who have died honourably in the service of their country."

Residents also spoke of their shock at the deaths.

Chris Roberts, 58, of Broyle Road, said: "I live just across the road and have always had a certain amount to do with the barracks.

"We always see military police going back and forwards to the shops and they are always very courteous and polite. They are very much a part of people's lives around here.

"People are very sad at the news."

Les Lewis, 30, landlord of the Punch House pub in East Street said: "The Military Police are an absolutely brilliant bunch.

"I know some of them pretty well to talk to, because we have quite a lot of squaddies come in at the weekend. I was expecting a really big crowd at the weekend but the parade is going to be quite a sombre affair."

In the Commons, Bob Russell, Liberal Democrat MP for Colchester, the regiment's home town, said: "This is the darkest day in the garrison's last 60 years and I am sure the whole House would wish to convey our condolences to the families of those six people."

Major Bryn Parry-Jones, commanding officer of 156 Provost Company, said: "The loss of six soldiers from such a small, tight-knit unit as 156 Provost Company clearly comes as a dreadful shock to us all, not only the friends and families of those killed, but also all those in the Royal Military Police who knew and worked with them."

Major Parry-Jones said all six men were highly professional soldiers and policemen, whose deaths illustrated the challenging situations the RMP faced.

"From the oldest, aged 41, to the youngest, aged 20, these soldiers had between them a wealth of operational experience and distinguished service.

"The circumstances surrounding this dreadful incident are still being investigated. At this time, our priority is giving all the support we can to the families and friends who are having to cope with the loss of loved ones.

"We ask our men and women to risk the ultimate sacrifice in the service of their country and it is the sad truth that sometimes that sacrifice comes to pass."