Cardinal Fernando Filoni encouraged Vietnamese priests to "find remote areas where people have yet to know God."
South African Cardinal Wilfrid Napier said the synod's relatio has put the prelates in "a position that is virtually irredeemable."
The Vatican's seven ambassadors throughout the Middle East will hold a summit at the Vatican this week that will be addressed by the Vatican's secretary of state, Cardinal Pietro Parolin, and Pope Francis.
Vatican spokesman Jesuit Fr. Federico Lombardi announced the convening of the Vatican officials, formally known as apostolic nuncios, in a short press briefing Tuesday.
While neither Lombardi nor a statement issued by the Vatican gives firm reasoning for the summit, it comes as focus around the world is centered on efforts to combat the Islamic State militant group.
Pope Francis wrote to the president of Iraq, calling for an end to the "brutal suffering of Christians and other religious minorities" and urging political leaders to end the humanitarian crisis in the country.
Francis said in his letter to Iraqi President Fouad Massoum: "I appeal to you with my heart full of pain while I follow the brutal suffering of Christians and other religious minorities who are forced to leave their homes, as their places of worship are destroyed."
Pope Francis' personal envoy to the suffering people of Iraq joined the Chaldean Catholic patriarch in launching an appeal to the international community Monday, pleading for help to liberate villages controlled by the Islamic State terrorists and to provide the displaced with international protection.
Pope Francis said the use of force can be justified to stop "unjust aggressors" such as Islamic State militants in Iraq, but he declined to endorse U.S. airstrikes.
Pope Francis formally asked U.N. agencies and the entire international community "to take action to end the humanitarian tragedy now underway" in northeastern Iraq.
In a letter signed Aug. 9 but released by the Vatican after it had been delivered, Pope Francis told U.N. Secretary-General Ban Ki-moon immediate action was needed "to stop and to prevent further systematic violence against ethnic and religious minorities."
Even as Francis called for peace in the Middle East, the Vatican tried to come to terms with the idea that U.S. military strikes were necessary and working.
Francis Chronicles: "One cannot generate hatred in God's name," Pope Francis said Sunday. "One cannot make war in God's name!"
Pope Francis is dispatching Cardinal Fernando Filoni as his personal envoy to northern Iraq, where Islamist militias have sent thousands of Christians and other religious minorities fleeing for their lives, the Vatican said Friday.
The Vatican announced the appointment of Filoni, a former papal nuncio to Iraq and Jordan, only a day after the pope launched a fresh appeal for the welfare of Christians affected by the violence there.