Vatican City. Two days after being discharged from the hospital, Pope Francis resumed his cherished Sunday custom of greeting the public in St. Peter’s Square, expressing thanks for the comfort he received after surgery and thanking the crowd shouting “Long live the pope!”

Before launching into prepared remarks, Francis expressed gratitude for "affection, attention and friendship" and the assurance of “the support of prayer” during his hospitalization for June 7 abdominal surgery at a Rome hospital to repair a hernia and remove increasingly painful scarring around his intestines.

“This human and spiritual closeness for me was a great help and comfort,'' Francis told some 15,000 people in the square. ”Thanks to all, thanks to you, thanks from the heart."

The 86-year-old pontiff sounded a bit breathless and hoarse at times, but he gestured frequently with his hands for emphasis, adlibbed at times from the prepared speech, and clearly looked delighted to be back to his routine.

While the thousands of Romans, tourists and pilgrims who regularly turn out for the weekly noon appearance of the pope at a window of the Apostolic Palace usually applaud when they catch sight of the pope at the window, this time the public’s applause seemed louder than usual. The three-hour surgery under general anesthesia had forced Francis to skip the Sunday appearance on June 11.

While his mood seemed uplifted to see the crowd below, including flag-waving nuns and tourists in sun hats on the hot, humid day, Francis turned somber as he noted that Tuesday marks World Refugee Day, an occasion promoted by the United Nations.

"With great sadness and so much sorrow I think of the victims of the very grave shipwreck that happened in recent days off the coast of Greece,'' Francis said. He was referring to the smugglers' overcrowded fishing boat, filled with hundreds of migrants, that sank in the Mediterranean Sea last week.

"It seems that the sea was calm,'' Francis said, seemingly expressing perplexity that such a grave tragedy could happen in those conditions.

"I renew my prayer for all those who lost their life, and I implore that, always, everything possible is done to prevent similar tragedies,'' the pontiff said.

Some of the 104 survivors said as many as 750 were aboard, leaving the possibility that hundreds perished. Greek rescuers recovered 78 bodies. Questions persist whether the Greek coast guard could have intervened in time to prevent the capsizing.

He also prayed for the young students “victims of the brutal attack” on a school in western Uganda. The attack by suspected rebels on a school in Uganda killed 42 people, including 38 students in their dormitories. Several were abducted near the border with Congo.

Francis lamented "this struggle, this war all over the place. Let us pray for peace."

He also urged people to remember the "martyred people in Ukraine,'' following Russia's invasion last year.

As he wrapped up his remarks and was about to leave the window, cries of “Long live the pope” in Italian rose from the crowd, and the pope quickly responded, “Thanks.”

The pope's doctors have urged him to take it easy as much as possible even as he resumes his Vatican workload. Francis will receive Brazil's president on Wednesday afternoon, the Vatican has announced. But to ensure his convalescence can proceed well, Francis won't conduct the Wednesday general audience in St. Peter's Square.

In early August, Francis will make a pilgrimage to Portugal for a youth jamboree. At the end of that month, he flies to Mongolia for a visit that will see him be the first pontiff to go to that Asian country.