European Commission vice president Frans Timmermans, a socialist candidate for the top commission post in EU elections, on Wednesday called for "no impunity" for priests who sexually abuse children.

Speaking in Warsaw, Timmermans, who has acknowledged he was sexually abused by a Catholic priest in the past, also urged other victims not to be silent or shamed.

His remarks came as a groundbreaking documentary on child sex abuse among Polish priests has sparked public outrage and a crisis in the devoutly Catholic country's church.

The film has put sexual abuse by members of the clergy in the spotlight as a key issue in Poland during the election campaign for the European Parliament. 

"To my church, the Catholic church: make sure there is no impunity, analyse the problem, like other churches in other countries have done, get to the bottom of it," said Timmermans, a Dutchman who leads the Social Democrats' campaign for the weekend elections. 

"If people engaged in criminal behaviour, denounce them to the authorities so that they can be prosecuted," Timmermans said.

The Dutch politician, 58, is vying to replace Jean-Claude Juncker as president of the European Commission.

He called for the church to undergo a "process of truth and reconciliation" over child sex abuse similar to "what happened after Apartheid in South Africa" insisting that "this is what our church needs."

Earlier this month, Pope Francis passed a landmark new measure to oblige those who know about sex abuse to report it to superiors, which could bring many new cases to light.

Posted on YouTube this month, the documentary "Tell No One" about child sex abuse by Polish priests has gone viral, sparking outrage that has rocked Poland's powerful Roman Catholic church.

The two-hour documentary includes hidden camera footage of victims who are now adults confronting elderly priests about the abuse they suffered decades earlier.

Several of the priests admit to the abuse and apologise for it, sometimes hinting at monetary compensation.

The film also details how priests accused or even convicted of child sex abuse were transferred and able to continue their duties and work with children. 

Top Polish clerics refused to be interviewed for the documentary but have since expressed deep regret about the abuse it has brought to light.

Poland's right-wing Law and Justice (PiS) government, which is closely allied to the church, more than doubled the maximum prison sentences for convicted paedophiles to 30 years in a hasty vote last week.

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