The panel of independent rights and legal experts fired questions at the Vatican delegation during Monday's opening session of a two-day hearing.
It was the first time the Vatican has been scrutinised since it signed up in 2002 to a global convention banning not only torture, but also other cruel, inhuman and degrading treatment and punishment.
"We all know that the Catholic Church is against violence," said committee member George Tugushi.
"Yet we can see that child abuse cases have not been addressed for decades," he said.
Fellow members demanded details of prosecutions by the Roman Catholic Church's canon law courts, its cooperation with national law enforcement in holding to account paedophiles in its ranks, and the extent of Vatican awareness of misdeeds in individual dioceses.
The Vatican delegation was to respond in depth at Tuesday's session, but its UN envoy Monsignor Silvano Tomasi on Monday insisted the Holy See was battling abuse.
The Church has been shaken by a decade-long cascade of scandals over abuse by priests and lay officials, from Ireland to the United States and Australia.
Hundreds of priests have been defrocked, and new cases continue to emerge, notably in Poland, Portugal and Latin America.
"We can wish that this did not happen. But human nature being what it is, it did," Tomasi said, underscoring that paedophilia was a global scourge not confined to the Church.
"Measures taken in the last 10 years by the Holy See and local Churches are bringing positive results," he said.
"Our concern is to prevent this and protect the children. The Church has to do the cleaning of its house. It has been doing it for the last 10 years," he added.
Actions, not words
Victim support groups insist that rape and molestation of children fall under the terms of the torture convention.
"The Vatican has signed up to a treaty and undertaken to prevent, punish and provide redress. But it has failed terribly. And not only has it failed, but in some cases it has acted completely contrary to those obligations," Katherine Gallagher, an attorney at the US-based Center for Constitutional Rights, told reporters.
Barbara Blaine, president of the 18,000-strong international Survivors Network of those Abused by Priests, said victims were used to "lofty statements" from the Vatican.
"They should be judged by their actions, not by what they say," Blaine told reporters.
"The vast majority of us would never have had our innocence shattered if Church officials had done the right thing," she added.
Victims hope the Vatican will face similarly-scathing criticism as in January, when the UN children's rights watchdog assessed it for the first time.
That panel condemned the Vatican for failing to do enough to stamp out abuse and for allowing systematic cover-ups, despite pledges to stem the problem.
'No safe haven'
The Church insists the UN anti-torture convention, like the children's rights accord, legally applies only to the territory of Vatican City.
"The Holy See has no jurisdiction over every member of the Catholic Church," Tomasi said.
"Persons who live in a particular country are under the jurisdiction of the legitimate authorities of that country and are thus subject to the domestic law and the consequences contained therein," he said.
But critics say the Vatican and individual dioceses have helped abusers escape justice by failing to report their crimes and transferring them to new parishes, sometimes abroad.
The committee vice-chair Felice Gaer said the Vatican should take responsibility for actions in the Church's branches worldwide.
"The convention aims to ensure there is no safe haven for perpetrators of torture, or cruel, inhuman and degrading treatment," she said.
Benedict XVI, pontiff from 2005 to 2013, was the first pope to apologise to abuse victims and call for zero tolerance. His successor Pope Francis has stepped up efforts.
The committee session came two days after a Vatican panel including US Archbishop Sean Patrick O'Malley and Irish victim and campaigner Marie Collins announced that it would develop "best practices" to curb abuse and protect minors.
But the Church faces a backlog of thousands of past cases.