VATICAN CITY—Pope Francis urged princes, presidents, sheiks and thousands of ordinary people gathered for his installation Mass on Tuesday to protect the environment, the weakest and the poorest, mapping out a clear focus of his priorities as leader of the world's 1.2 billion Catholics
 

The Argentine native is the first pope from Latin America and the first named for the 13th-century friar St. Francis of Assisi, whose life's work was to care for nature, the poor and most disadvantaged. Echoing the gentleness for which St. Francis is known, the pope said a little bit of tenderness can ``open up a horizon of hope.''
 

The Vatican said between 150,000-200,000 people attended the Mass, held under bright blue skies after days of chilly rain and featuring flag-waving fans from around the world. In Buenos Aires, thousands of people packed the central Plaza di Mayo square to watch the celebration on giant TV screens and erupted in joy when Francis called them from Rome, his words broadcast to the crowd over loudspeakers.
 

“I want to ask a favor,'' Francis told them. “I want to ask you to walk together, and take care of one another. ... And don't forget that this bishop who is far away loves you very much. Pray for me.”
 

Back in Rome, Francis was interrupted by applause several times during his homily, including when he spoke of the need to protect the environment, serve one another with love and not allow ``omens of destruction,'' hatred, envy and pride to ``defile our lives.''
 

Francis said the role of the pope is to open his arms and protect all of humanity, but ``especially the poorest, the weakest, the least important, those whom Matthew lists in the final judgment on love: the hungry, the thirsty, the stranger, the naked, the sick and those in prison.''
 

“Today amid so much darkness we need to see the light of hope and to be men and women who bring hope to others,'' he said. ``To protect creation, to protect every man and every woman, to look upon them with tenderness and love, is to open up a horizon of hope, it is to let a shaft of light break through the heavy clouds,'' he said.
 

Francis, 76, thrilled the crowd at the start of the Mass by taking a long round-about through the sun-drenched piazza and getting out of his jeep to bless a disabled man. It was a gesture from a man whose short papacy so far is becoming defined by such spontaneous forays into the crowd and concern for the disadvantaged.
 

The blue and white flags from Argentina fluttered above the crowd, which Italian media initially estimated could reach 1 million. Civil protection crews closed the main streets leading to the square to traffic and set up barricades for nearly two kilometers along the route to try to control the masses and allow official delegations through. 
 

Before the Mass began, Francis received the fisherman's ring symbolizing the papacy and a woolen stole symbolizing his role as shepherd of his flock. He also received vows of obedience from a half-dozen cardinals _ a potent symbol given his predecessor Benedict XVI is still alive and was reportedly watching the proceedings on TV from the papal retreat in Castel Gandolfo. 
 

A cardinal intoned the rite of inauguration, saying: ``The Good Shepherd charged Peter to feed his lambs and his sheep; today you succeed him as the bishop of this church.''
 

Some 132 official delegations attended, including more than a half-dozen heads of state from Latin America, a sign of the significance of the election for the region. Francis has made clear he wants his pontificate to be focused on the poor, a message that has resonance in a poverty-stricken region that counts 40 percent of the world's Catholics.
 

In the VIP section was German Chancellor Angela Merkel, U.S. Vice President Joe Biden, the Argentine President Cristina Fernandez, Taiwanese President Ying-Jeou Ma, Zimbabwe President Robert Mugabe, Prince Albert of Monaco and Bahrain Prince Sheik Abdullah bin Haman bin Isa Alkhalifa, among others. All told, six sovereign rulers, 31 heads of state, three princes and 11 heads of government were attending, the Vatican said. (AP)