VATICAN CITY  (Reuters) - Pope Francis, acting to end years of scandals damaging the Catholic Church, overhauled Vatican law on Thursday to specify sexual violence against children as a crime and impose tough penalties for staff who leak confidential Vatican information.

Issuing a "Motu Proprio", a decree of his own initiative, Francis also said he would renew the Holy See's commitment to international conventions against organised crime and terrorism.

Under the changes, sexual violence and sexual acts with children, child prostitution and child pornography are cited in a broader definition of crimes against minors and punishable by up to 12 years in prison, a Vatican document showed.

Francis, who succeeded Pope Benedict in March, inherited a Church struggling to restore its credibility after a spate of scandals including the molestation of children by priests in a number of countries and an investigation into suspected money-laundering at the Vatican's bank.

The legal changes apply only within the Vatican City state but are meant to demonstrate that Francis is taking the various scandals seriously and aims to align Church policy with international legal standards.

The Survivors Network of Those Abused by Priests (SNAP) was unimpressed, saying his initiative might burnish the Vatican's image but "in the real world this changes virtually nothing (as it affects only) the 0.2 square miles of Vatican property".

SNAP urged the Church hierarchy to focus on having its personnel abide by long-established secular laws on sexual abuse and rooting out bishops who failed to protect children.

The Vatican was also shaken last year by the "Vatileaks" affair in which Benedict's butler, Paolo Gabriele, was convicted for stealing personal papal documents and leaking them to the media. He was pardoned by Benedict after being briefly jailed.

LITANY OF GRAFT, MISMANAGEMENT

Before abdicating in February, Benedict left Francis a top-secret report about leaks of the internal documents that alleged corruption, mismanagement and infighting in the Vatican administration.

Francis's decree includes stricter rules governing the disclosure of secret information or documents and stipulates a punishment of up to eight years in prison if they concern the "fundamental interests" of the Holy See, or Church government.

Pope Francis also said United Nations conventions on transnational organised crime, illegal drug trafficking and terrorism financing would be implemented as part of the changes.

Giuseppe Dalla Torre, president of Vatican City tribunal, said the state's penal system, based on Italian penal codes from 1889 and 1913, had been updated to deal with more modern crimes.

"The evolution of society and the economy, and the phenomenon of globalisation have shown that there is a need to provide for new situations," he told a news conference.

"The problem of laundering dirty money is evidently a problem linked on one side with the globalisation of the economy and on the other side to the expansion of a certain type of financial economy," he said.

The Vatican's bank, a byword for opaque and secretive dealings for decades, is at the centre of an investigation by Italian prosecutors looking into money laundering.

A report by Moneyval, a department of the Council of Europe, last year identified failings in the bank and gave the Holy See a negative rating in several transparency-related criteria.

In June Francis set up a special commission of inquiry to reform the bank, seeking to get to grips with an institution that has embarrassed the church. The group held its first meeting on Thursday with the pope attending, according to the Vatican newspaper Osservatore Romano.

(Editing by Mark Heinrich)