Pope John Paul II slipped towards death Friday after a devastating heart attack as the Vatican called on the world's Roman Catholics to pray for their spiritual leader. The Vatican spokesman Joaquin Navarro-Valls was somber late Friday:

"The general conditions and cardio-respiratory conditions of the Holy Father have further worsened," Navarro-Valls said in a statement to reporters at the Vatican. The 84-year-old pontiff was also experiencing a "gradual worsening" of his blood pressure "and breathing has become shallow," Navarro-Valls said. Doctors treating the pope had also noted "renal insufficiency," according to the statement.

"The biological parameters are notably compromised," it said, adding the "Holy Father -- with visible participation -- is joining in the continual prayers of those assisting him."

The statement was delivered as thousands of people attended a special mass in Rome's Saint John in Lateran Cathedral. Aross the world, from his native Poland to Indonesia via the Middle East, thousands of faithful also prayed for the pontiff who has led the world's 1.1 billion Catholics for more than a quarter of a century.

Hours earlier, the Vatican had said the pope's condition was "very serious" following a heart attack, septic shock and a urinary tract infection, and although by midday he was reported to be stable, a senior cardinal said he was "abandoned to the will of God."

Navarro-Valls, who has been the spokesman for John Paul II since late 1984, was visibly moved when asked for his personal feelings. "It's an image which I had never before seen in 26 years ... the pope lucid and extraordinarily serene, with the expected breathing difficulties," he said in a voice broken by emotion.