The Vatican has come under intense pressure from a UN panel to explain its handling of clerical sex abuse as its representatives were questioned on the global scandal at length for the first time in public.

Experts from the UN's committee on the rights of the child grilled a delegation from the Holy See, which is regarded as a sovereign entity, yesterday, as victims of sex abuse by priests flew into Geneva to watch the proceedings.

As the hearing got under way, Archbishop Silvano Tomasi, the Holy See's envoy to the UN, made it clear that there was no excuse for violent or exploitative behaviour towards children. "Such crimes can never be justified, whether committed in the home, in schools, in community and sports programmes, in religious organisations structures," he said.

But he kept to the line that the Holy See was distinct from the global Catholic church and had little jurisdiction in countries beyond the Vatican city state. The guidelines already put in place by the Holy See and Catholic churches around the world had, when properly applied, presented a way of eliminating the scourge of abuse, he said.

"Priests are not functionaries of the Vatican," Tomasi told the committee. "Priests are citizens of their own states, and they fall under the jurisdiction of their own country." However, he added that the Vatican would welcome any suggestions from the committee that would assist it in ensuring "efficient implementation" of reforms.

Those suggestions – and a torrent of questions relating to the Catholic church's response, past and present, to the scandal – were not slow in coming.

Experts interrogated the Holy See on many issues, including an alleged lack of transparency in its handling of abuse cases and their aftermaths, punishment of abusers that was often insufficient, and inadequate co-operation with civil judicial authorities.

Questioned about an instance from 2001, when Cardinal Darío Castrillón Hoyos, a then senior Vatican official, praised French bishop Pierre Pican for not reporting to civil authorities a priest in his diocese who had raped a boy, Charles Scicluna, a former sex crimes prosecutor for the Vatican and auxiliary bishop of Malta, indicated this was an area on which the Holy See knew the approach had to change.

Pointing out that the example was from more than a decade ago, he said: "The Holy See gets it. Let's not say 'too late' or not. There are certain things that need to be done differently." He added: "It is not a policy of the Holy See to encourage cover-ups." He also insisted that the Holy See "willingly collaborates" with the judicial authorities in civil states.

But his words did not convince Pam Spees, of the US-based advocacy group the Centre for Constitutional Rights, who said the Vatican's "performance" was unsurprising. "The Vatican attempted to relegate the issue to the past and claim it is a new era, that they now 'get it,' but they continue to refuse to turn over records for prosecution, punish higher-ups that covered up the crimes, or provide any real evidence that they are now putting the safety of children above the reputation of the Church," she said.

"Nonetheless, today's hearing is a milestone in calling for an end to these days of impunity. The international community is demanding answers, and that is the first step toward true accountability and, we hope, an end to the widespread violence against children."

The delegation's appearance in Geneva was a mandatory part of the Holy See's duties as a signatory of the UN convention on the rights of the child, which it ratified in 1990. The build-up to the hearing had already been hit by controversy when, in December, the Holy See refused to provide detailed information requested on abuse cases and specific information concerning their handling and investigation, citing confidentiality norms.

Yesterday, as the panel began a day of questioning, it showed little sign of wanting to indulge the delegation. Some statements appeared to be welcomed, but the Holy See was urged to take more "concrete, visible actions" to push ahead with its efforts to tackle the problem.

One expert asked specifically about the Vatican's handling of two cases that have caused particular embarrassment to the church: one from the past, that of the sexual scandals of the disgraced Legion of Christ founder Marcial Maciel, and another, which is ongoing, concerning Archbishop Jozef Wesolowski, the former apostolic nuncio (ambassador) to the Dominican Republic. Wesolowski was recalled to Rome this summer after facing accusations of abusing teenage boys.

Other experts focused on why in the past abusive priests had been simply moved from one area to another and often allowed to have more contact with children. Scicluna said that "offender mobility [was] a grave concern", adding that dioceses and parishes were now obliged to pass on information concerning a priest wanting to move on.

In their remarks, both Scicluna and Tomasi said the Catholic church was keen to become "an example of best practice" in the sphere of child protection. They said that changes – including a set of guidelines unveiled in 2011 – provided a framework for effective handling of the problem.

But Scicluna acknowledged that it was "a work in progress" and that "more transparency and accountability on the local level" was needed. Last month Pope Francis announced the establishment of a new committee to fight clerical sex abuse, a direct result of consultation with cardinal advisers from outside the Vatican.