The leaders of Spain and Turkey pledged at a meeting of world religious and cultural figures on Sunday to seek to defuse the extremism that led to al Qaeda's September 2001 attacks on the United States.
The three-day UN-sponsored gathering at the Mediterranean island resort of Palma de Majorca, backed by Secretary-General Kofi Annan, aims to forge a cross-cultural Alliance of Civilisations.
Spanish Prime Minister Jose Luis Rodriguez Zapatero and Turkish Prime Minister Tayyip Erdogan - their countries both targets of al Qaeda bombings that killed scores of people - co-sponsored the effort and spoke.
"We must stop up the springs of extremism, win the battle of ideas and principles, feed peace-seeking minds, strengthen the instinct of co-operation in our hearts," said Zapatero, elected days after bombings in Madrid killed 191 people in March 2004.
Erdogan, himself convicted of Islamist sedition before becoming Turkey's prime minister, said extremism was not confined to any one religion and terrorists might attack any target regardless of its culture.
Turkey, a Muslim country seeking admission to the European Union, was rocked by four al Qaeda bombs in Istanbul in 2003 that killed more than 60 people.
"Together we are planting a seed for an Alliance of Civilisations to grow in our world, and this will help the seeds of hundreds of thousands of Alliances of Civilisations to flourish," Erdogan told a news conference.
Zapatero suggested the idea last year in a speech at the United Nations. Annan gave it his backing in July.
The UN-supported group is due to report a plan by the second half of 2006, Zapatero said. The group should focus on mobilising opinion leaders, artists, the media, sports figures, scientists and others, he said.
Co-chairmen are former UNESCO Director-General Federico Mayor Zaragoza and Mehmet Aydyn, Turkey's minister for Turkish populations outside the country.
Erdogan and Zapatero left after the start of the session to attend the Euro-Mediterranean summit in Barcelona, Spain.