NAIROBI - Pope Francis said on Thursday in Kenya, a country that has seen a spate of attacks by Islamist militants, that dialog between religions in Africa was essential to teach young people that violence in God's name was unjustified.Bridging divisions between Muslims and Christians is a main theme of his first tour of the continent that also takes him to Uganda, which like Kenya has seen a number of Islamist attacks, and the Central African Republic, riven by sectarian conflict.sign up to our newsletterStarting his first full day in the Kenyan capital, Francis met Muslim and other religious leaders before saying an open-air Mass for tens of thousands of rain-drenched people who sang, danced and ululated as he arrived in an open popemobile."All too often, young people are being radicalized in the name of religion to sow discord and fear, and to tear at the very fabric of our societies," he told about 25 religious leaders.Inter-religious dialog "is not a luxury. It is not something extra or optional, but essential," he told them, stressing that God's name "must never be used to justify hatred and violence."He referred to Somalia's al Shabaab Islamists' 2013 attack on Nairobi's Westgate shopping mall and this year's assault on Garissa university. Hundreds of people have been killed in the past two years or so, with Christians sometimes singled out by gunmen.The chairman of the Supreme Council of Kenya Muslims, Abdulghafur El-Busaidy, called for cooperation and tolerance. "As people of one God and of this world, we must stand up and in unison," he told the pope.CONTRASTSFrancis's African tour is also addressing the continent's fast-growing Catholic population, which is expected to reach half a billion by 2050.A third of Kenya's 45 million people are Catholics. Tens of thousands of them gathered in pouring rain from before dawn to attend the pope's open-air Mass in central Nairobi.Representatives of Kenya's tribes ascended the papal altar platform to read prayers, their native dress contrasting with that of bishops in Western liturgical vestments just feet away.In his homily at the Mass, Francis urged the faithful "to resist practices which foster arrogance in men," speaking in a nation rattled by a series of corruption scandals.President Uhuru Kenyatta, a Catholic who attended the Mass, reshuffled his cabinet this week after several ministers were embroiled in graft allegations.When not in his popemobile, the pope, who has shunned many of the perks at the Vatican, was driven in a Honda car, starkly different to the Mercedes and other luxury vehicles used by top officials in Kenya where many people live in city slums or villages without electricity.Giving his address at Mass in a sodden sports field at Nairobi University, the pope urged youths on a continent with a large young population to resist the "new deserts created by a culture of materialism and indifference" and build a more just society.