Rome, Italy - Pope Francis, hospitalized for bronchitis four days ago, faces a "complex clinical picture" that will require the 88-year-old to stay longer than originally expected, the Vatican said on Monday.

After initially canceling events through Monday, the Vatican said the pope's weekly Wednesday audience would not go ahead either.

"The results of the tests carried out in recent days and today have demonstrated a polymicrobial infection of the respiratory tract that has led to a further change in treatment," it said in a statement.

"All the tests carried out until now are indicative of a complex clinical picture that will require adequate hospitalization."

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Vatican spokesman Matteo Bruni had earlier told reporters that the pope was in "good humor," had rested well overnight, had eaten breakfast, and read the newspapers.

A source in the pope's entourage had also insisted there was no alarm within the Vatican following his Friday admission to Rome's Gemelli hospital.

Francis was admitted after a "very busy" two weeks, during which "he was weakened," the source told AFP, but added: "There is no alarmism."

A Vatican source told AFP the pope was receiving oxygen.

Yet the news of the more complex situation raises fresh concerns about the Argentine pontiff, who has suffered increasing health issues in recent years.

In the days before his admission, Francis had admitted to difficulty breathing and had asked aides several times to read his speeches aloud on his behalf.

At his weekly general audience last Wednesday, he said he "cannot yet" read his own speeches, adding with a smile: "I hope that next time I can."

But he had continued taking meetings, including one with the prime minister of Slovakia on Friday morning, shortly before he headed to the hospital.