In a strong message days before a summit of U.S. churchmen on a sex abuse scandal, Pope John Paul II said Saturday that priests must live celibate lives and avoid scandalous behavior. Bishops, he said, must investigate such behavior and take action to end it.

In comments to Nigerian bishops, the pope didn't directly refer to the scandal rocking the American Church. But the timing of his message appeared to be a clear signal of his position going into the summit and a firm policy statement that he doesn't tolerate the type of behavior shown by some American churchmen.

The scandals, in which several churchmen have been accused of abusing children and teenagers, have shaken confidence in the American Church, cost it millions of dollars in settlements and raised questions about bishops' mishandling of the investigations.

The pope summoned American cardinals to a summit Tuesday and Wednesday to discuss the matter — an extraordinary measure that has underscored the urgency that the Vatican now appears to feel is necessary to deal with the issue.

In his comments to the Nigerians, the pope didn't refer to sex offenders or pedophilia, focusing on the broader issue of the need for priests to live a life of poverty and celibacy.

The Vatican has spoken out about problems in the African Church of priests breaking their vow of celibacy and having relations with women.

"The value of celibacy as a complete gift of self to the Lord and his Church must be carefully safeguarded," John Paul told the Nigerians.

"Behavior which might give scandal must be carefully avoided, and you yourselves must diligently investigate accusations of any such behavior, taking firm steps to correct it where it is found to exist," he said.

John Paul's comments Saturday were his most extensive remarks about celibacy since the revelations of sex abuse began pouring out in the United States earlier this year. He broke his long silence in a pre-Easter letter to priests last month, decrying the scandal caused by some.

In the meetings this week, the cardinals will be looking to the Vatican for guidance and backing on a wide range of issues, foremost among them whether the church should ever consider reassigning sex offenders and creating a uniform American policy for reporting abuse claims to police.

In the United States, the Church is accused of covering up misconduct by priests, in some cases by moving known abusers from job to job.

Cardinal Bernard Law, head of the Boston archdiocese, has faced growing criticism since acknowledging he transferred a priest to another parish despite knowing of sexual misconduct allegations against the man. That defrocked priest later was sentenced to prison.