An anti-racism group said that a verbal abuse provoked the France captain and forced him to head-butt Materazzi in the chest with just 10 minutes remaining in extra time on Sunday.

"According to Several well informed sources from the world of football, it seems that Materazzi called Zidane a 'Dirty terrorist'," French SOS foundation said in a report published on their website on Monday.

"If such assumption is right it'd be considered as racist act by the Italian defender and, as a result, we demand a full investigation by FIFA in the matter."

Zidane, a son of Algerian immigrants who has been inspiring the French football over the past decade, was shown a straight red card after he was spotted by the fourth referee hitting his Italian marker.

Television replays showed a verbal spat between the duo before the often-cool Zidane turned around, approached Materazzi and head-butted him to leave the Inter Milan aggressive man sprawling on the grass in pain.

The 34-year-old playmaker, set to retire from the game after the tournament, walked off the pitch in disgrace with tears in his eyes as his farewell party turned into a tragedy.

Materazzi, though, denied the accusation.

"It is absolutely not true, I did not call him a terrorist," Materazzi told Italian News Agency ANSA. "I'm ignorant. I don't even know what the word means."

Experts in reading lips also rejected the racism story but said Materazzi insulted Zidane's sister twice during their heated exchange.

Brazilian network Globe consulted specialists in the issue and they said Materazzi called Zidane's sister a "prostitute" in a couple of occasions, Spanish paper Marca reported.

No comment has been issued by Zidane who reportedly refused to talk about the incident in the dressing room after France lost the final 5-3 on penalties.

Zidane's agent Alain Migliaccio told BBC Sport that he knew that his client was provoked by Materazzi.

"He told me that Materazzi said something very serious to him but he wouldn't tell me what," he said.

But Migliaccio revealed that Zidane will talk about the incident in full details later this week.

Although many believe Zidane's dismissal ended Les Bleus dreams of winning the World Cup, the France number 10 was received like heroes back home.

Thousands of French fans chanted supporting slogans to Zidane, carried his shirt and photos when the team arrived in Paris as they were received by President Jacques Chirac.

"In such a hard and intense moment for you, I would like to express the whole nation's affection and admiration for you," an emotional Chirac said addressing Zidane.

"You are a virtuoso, a genius of football and an exceptional human being. That is why France admires you."