Heads of state and government from several countries have joined experts on terrorism and security at a conference in Madrid that seeks to identify the causes of extremist violence and explore ways to reduce the threat. The four-day gathering coincides with the first anniversary of last year's train bombings in the Spanish capital that killed 191 people.

Kings, presidents and prime ministers are attending the Madrid meeting, along with international figures like United Nations Secretary General Kofi Annan.

The conference has been organized by the Club of Madrid, a non-governmental organization grouping dozens of democratically elected former presidents and prime ministers.

The gathering is expected to focus on four main areas: the causes of terrorism; the response to the threat by security forces; how terrorism challenges democracy; and how civil society can be strengthened to confront it.

Conference organizer Christer Elverson says the aim of the symposium is to bolster international cooperation against terrorism in practical ways.

"We believe that terrorism is a global phenomenon," said Christer Elverson. "We believe the only way to tackle a global phenomenon is by going global - international cooperation - making sure that all countries that have been hit work together."

A group of former statesmen and anti-terrorism experts is expected on Friday to release a plan of action on how best to combat terrorism in the years ahead. A diplomat monitoring the meeting says the group's conclusions are likely to reflect a European approach based on prevention rather than what he called the American strategy of reaction and retaliation.

The diplomat says the group will stress engaging Muslim nations, increasing development aid, and stepping up efforts to assimilate immigrants into host nations.

Just before the conference opened on Tuesday, Spanish authorities announced that they had arrested a 23-year-old Moroccan allegedly linked to the Islamic terror cell that carried out last year's March 11 train bombings in Madrid. There are now 23 people detained in Spain in relation to those blasts, which constituted the worst terrorist attacks in western Europe's modern history.