"In recent days, a report was made public which detailed the experiences of at least a thousand survivors... the abuse of power and of conscience at the hands of priests," the pope said in a letter made public by the Vatican.
"Even though it can be said that most of these cases belong to the past, nonetheless as time goes on we have come to know the pain of many of the victims," he said.
"We have realized that these wounds never disappear and that they require us forcefully to condemn these atrocities and join forces in uprooting this culture of death," he added.
Vatican spokesman Greg Burke said: "Pope Francis says greater accountability is urgently needed, not only for those who committed these crimes but also for those who covered them up – which in many cases means bishops."
However, Irish abuse survivor Marie Collins, who last year quit the pope's panel on child protection, said the latest statement from the Vatican lacked a "plan of action".
"Statements from Vatican or pope should stop telling us how terrible abuse is and how all must be held accountable. Tell us instead what you are doing to hold them accountable," she said in a tweet.
"That is what we want to hear. 'Working on it' is not an acceptable explanation for decades of 'delay'," she added.
A devastating US grand jury report published last week decried a systematic cover-up by the Catholic Church.
The grand jury said that more than 1,000 child victims were identifiable, but that the actual number was "in the thousands".
The report is thought to be the most comprehensive to date into abuse in the US church since The Boston Globe first exposed paedophile priests in Massachusetts in 2002.
Calling for "solidarity" with the victims and a fight against "spiritual corruption", Pope Francis said "no effort to beg pardon and to seek to repair the harm done will ever be sufficient.
"With shame and repentance, we acknowledge as an ecclesial community that we were not where we should have been, that we did not act in a timely manner, realizing the magnitude and the gravity of the damage done to so many lives," he said.
Pope Francis ended the letter by exhorting Catholics to "fasting and prayer", in order to "open our ears to the hushed pain felt by children, young people and the disabled".
It's not the first time that Francis, who became pope in 2013, has had to react to the scandal of child abuse within the Church.
At the end of July he accepted the resignation of prominent US cardinal Theodore McCarrick, who has been accused of sexually abusing a teenager nearly 5 decades ago.
Among senior church members in the US forced to resign for protecting paedophile priests were the late cardinal Bernard Law in Boston and cardinal Roger Mahony in Los Angeles.
On Monday Burke acknowledged that the scandal went further than the United States, citing Ireland – where Pope Francis is expected on a visit this weekend – and Chile as other examples of countries where widespread abuse allegations have been made.
"Pope Francis has written to the people of God, and that means everyone," Burke said.
In May the third-highest member of the Vatican hierarchy, Australian George Pell, was ordered to stand trial on "multiple" historical sex charges, which he denies.
His case coincided with an Australian public enquiry that found that 7% of priests were accused of paedophilic acts between 1950 and 2010. – Rappler.com