BBC: Saudi Arabia's monarch has urged Muslims to speak with one voice in preparation for interfaith dialogue with the Jewish and Christian worlds.
King Abdullah was speaking at a three-day conference in Mecca, attended by hundreds of Muslim delegates.
The king, whose country is mainly Sunni Muslim, said extremists were exploiting the tolerant nature of Islam.
As well as extremism, delegates hope to tackle what is seen as the negative perception of Islam in the West.
BBC Arab affairs analyst Magdi Abdelhadi says the meeting is supposed to be the Saudi answer to the controversial "clash of civilizations" thesis of US academic Samuel Huntington.
Muslim writers often cite Prof Huntington's ideas as evidence of Western hostility to Islam in particular.
'Voice of justice'
King Abdullah entered the hall alongside Iranian politician Akbar Hashemi Rafsanjani, who sat beside him on the stage.
Correspondents say the message was that the Sunni kingdom was now in agreement with moderate Shia Muslims such as Mr Rafsanjani, a former Iranian president.
"You have gathered today to tell the whole world that... we are a voice of justice and values and humanity, that we are a voice of coexistence and a just and rational dialogue," King Abdullah told the delegates.
Extremism was a challenge to Islam that targeted the "magnanimity, fairness and lofty aims" of the religion, he said.
"That's why this invitation was extended - to face the challenges of isolation, ignorance and narrow horizons, so that the world can absorb the good message of Islam." Saudis Launch Islamic Unity Drive >>> | June 4, 2008
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Saudi King: End Islamic Extremism >>> (Associated Press) | June 4, 2008
The Dawning of a New Dark Age (Paperback - UK)
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