By Philip Pullella and Sylvia Westall
ABU DHABI (Reuters) - Pope Francis became the first pontiff to visit the Arabian Peninsula on Sunday, just hours after issuing his strongest condemnation yet of the war in Yemen, where his host the United Arab Emirates has a leading military role.
Shortly before departing for Abu Dhabi, Pope Francis said he was following the humanitarian crisis in Yemen with great concern, using his regular Sunday address in Vatican City to urge all sides to implement a fragile peace deal and help deliver aid to millions of hungry people.
"The cry of these children and their parents rise up to God," he told tens of thousands of people in St. Peter's Square.
"Let us pray strongly because they are children who are hungry, who are thirsty, they don't have medicine and they are in danger of death," he said before boarding his flight.
Television footage showed Francis being greeted on arrival by Abu Dhabi's Crown Prince Sheikh Mohammed bin Zayed al-Nahyan, who escorted him to meet Sheikh Ahmed al-Tayeb, the Grand Imam of Egypt's Al-Azhar mosque, whom the pontiff embraced.
Both men will hold meetings with Pope Francis on Monday.
The UAE plays a leading role in the Saudi-led coalition battling the Iran-aligned Houthi group to restore the internationally recognised government in the nearly four-year war that has pushed Yemen to the brink of famine.
The United Nations is trying to implement a truce and troop withdrawal deal in the main Yemeni port of Hodeidah that was agreed in December talks as a trust-building step that could pave the way for political negotiations to end the conflict.
Vatican officials have said it is not clear whether Pope Francis will address the sensitive subject in public or private during his visit to Abu Dhabi, which is aimed at promoting interfaith dialogue.
The pope will meet Muslim leaders and celebrate an outdoor mass for some 120,000 Catholics. He has said the trip, which ends on Tuesday, is an opportunity to write "a new page in the history of relations between religions".
The UAE, which named 2019 its Year of Tolerance, says the visit reflects its history as a "cradle of diversity".
But it faces criticism from human rights groups for jailing activists, including Ahmed Mansoor, an Emirati who is serving a 10-year sentence for criticising the government on social media.
"We are calling on Pope Francis to raise the issue of their incarceration with his hosts, and urge their immediate and unconditional release," Amnesty International said in a statement on Saturday.
UAE authorities did not immediately reply to a request for comment.
Priests and diplomats describe the UAE as one of the most open environments in the Gulf for Christian worship. But like its neighbours, the UAE does not allow dissent or criticism of its leadership.
The UAE is home to around half of an estimated two million expatriate Catholics living in the peninsula, a territory which also hosts Islam's holiest sites in Saudi Arabia.
All Gulf states except Saudi Arabia allow Christian worship in churches or church compounds and other premises with special licences. In Saudi Arabia, non-Muslims pray in secret gatherings in private homes and embassies.
Abu Dhabi's crown prince is an ally of Saudi Arabia's Crown Prince Mohammed bin Salman, who has reached out to Christian representatives abroad as part of attempts to open up the conservative kingdom.
The pope has already visited half a dozen predominantly Muslim nations during his reign, using the trips to call for inter-religious dialogue and to condemn the use of violence in the name of God.
The UAE ambassador to Washington, Yousef Al Otaiba, wrote in an op-ed in Politico magazine on Sunday that the pontiff's visit sent a signal of co-existence and respect in the face of the "menace of extremism" across the Middle East.
(Editing by Gareth Jones)