By Marcus George BBC News Online

In the week that the beautiful game brought ugly scenes onto the hallowed turf at Old Trafford, it's not exactly the most auspicious occasion to talk about the peace-enhancing properties of football.

Sven and Nancy hope to bring world peace through football

For the game which has nurtured a tradition of fighting off the pitch, as well as on, football's newly created role comes as even more of a surprise.

Earlier this month English fans were warned they could die should they ignore a restriction on them travelling to Turkey to watch England's European Cup qualifier.

But United Nations, move aside. Nancy are Sven have stepped onto the stage of conflict resolution and the chief weapon in their locker room is the game of football itself.

The soccer celebrities have this week launched Truce International - an attempt to end conflict around the world, through the beautiful game.

The power of football

The idea is that for one day every year, soldiers and militants down their weapons of war to show their might and verve through their nimble footwork.

Yet despite the relentless discourse on the violence of football, the positive power of sport has never been underestimated.

The co-operation of Japan and Korea in hosting the 2002 World Cup built bridges between the two nations who relationship has been strained since the Japanese colonization of Korea in 1910.

The football governing body Fifa was even nominated for the Nobel peace prize in 2001 for its role in facilitating international relations.

In sport, people's identities become more rigid. Their perceptions can become more negative." John Williams

South Africa's victory in the 1995 Rugby World Cup is said by many commentators to have united a fragmented South African society.

When Nelson Mandela sported a Springboks rugby shirt - a sport associated with white colonizers - it was the symbolic dawning of a new era in South African society.

And now Olympic authorities are desperately trying to promote a complete ceasefire in hostilities during the 2004 Olympic games.

The idea is a return to the ancient Greek tradition of ekecheiria or "Olympic Truce", which calls for an end to all conflicts during the games.

'Good luck Sven'

But can football really give peace a chance? Highly unlikely, says John Williams, the director of Leicester University's Sir Norman Chester Centre for Football Research.

"Good luck to Sven if he thinks that sport can deliver peace," said John. "But probably, deep down in his heart, he knows it can't."

"The problem is that football comes with all kinds of complexities and ambiguities. By defining your connection to a particular club you're defining an identity.

"In sport, people's identities become more rigid. They identify with those closer to them and not with the opposition. Their perceptions can become more negative."

Would these Liberian fighters put down their weapons for football?

But Mr Williams says football has significant positive powers too, citing its ability to promote social cohesion on a community level.

Sports in Ireland also provided interesting case studies for sociologists, he said. The Irish rugby team and boxing in Ireland were both successful examples of sports leaving sectarian differences behind.

But there's a thin line between success and failure.

Neil Lennon was hounded out of the Northern Ireland national team by a hardcore of protestant fans unhappy about the prominent role of a Celtic player - a club with historical Irish Catholic roots.

This wasn't always the case. At first supporters were pleased to see the footballer playing across the sectarian divide.

The race row within South Africa's rugby squad ahead of this year's World Cup is threatening to undo all the efforts of making rugby accessible to black players and fans.

"Football mostly offers a flag for the celebrating of differences and there are plenty more examples," says John Williams, adding the issues of gender and race to the boiling pot.

"Sport might appear to be doing social good and, in some respects, it is. But at the same moment it's also making social and ethnic divisions more concrete.

"In sport those who 'belong' are immediately set against those who, clearly, don't.

So can the Ice Man really put a freeze on global conflict?