The UN's chief met the ecumenical patriarch of Constantinople on Friday as the UN food agency was looking for support from world religious leaders in the fight against global hunger.
"Eradicating hunger not only makes economic and political sense, it is also a moral issue," Food and Agriculture Organisation director-general Jose Graziano da Silva was quoted in a FAO statement as saying at the meeting.
The FAO chief met Bartholomew I, a noted environmentalist, in Istanbul.
In his letter to the mosque's Grand Imam Sheikh Ahmed Mohamed el-Tayeb, Graziano da Silva asked for support in efforts to eradicate global hunger and informed him of FAO's activities in the drought-prone Horn of Africa.
"We must achieve global food security in order to have a more secure world," Graziano da Silva was quoted as telling the grand imam.
Similar letters will be sent to other religious leaders, the FAO said.
In June, Graziano da Silva was received in a private audience by Pope Benedict XVI in which he called for "renewed support of the Catholic Church in the fight against hunger at the global and local levels".