The Vatican's secret archives on Pius XII should be ready for opening in about five years and will clear him of accusations that he turned a blind eye to the Holocaust, the archives' head said on Thursday.

"He was a great pope, who, as you know, is under attack for his presumed silence on the Shoah," said Monsignor Sergio Pagano, using the Hebrew word for the Holocaust. "But in reality he did many things for Jews and for prisoners of World War Two".

Some Jews have accused Pius, who reigned from 1939 to 1958, of not doing enough to help Jews, a charge his supporters and the Vatican deny.

Jews have for years been calling on the Vatican to open the archives as soon as possible so they can be studied by scholars and have asked Pope Benedict to freeze the process that could make Pius a saint until all the archives can be examined.

Pagano said 20 Vatican archivists were working full time on the millions of pages of documents in more than 15,000 bundles regarding Pius's papacy.

He said five or six more years of work are needed to prepare and catalogue the archives. Pagano said he believes they should be open to everyone.

"There will be some nice surprises, even as far as the Jews are concerned," Pagano said, adding that the pope did not remain inactive when Jews were rounded up for deportation on October, 1943.

"Pope Pius took great risks, even very great personal risks, to save Jews. I can't say more now but whoever wants to open their eyes in five or six years will be able to open them," he said.

The Vatican maintained that Pius worked quietly behind the scenes because direct interventions may have worsened the situation for both Jews and Catholics in Europe. Many Jews have rejected this position.

Pope Benedict has come under great pressure from both the Catholic and Jewish side over the possible sainthood of Pius.

Catholic supporters of Pius have been pushing him to speed up the process while most Jews believe making Pius a saint would irrevocably harm Catholic-Jewish relations.

The Vatican's saint-making department in 2007 voted in favour of a decree recognising Pius's "heroic virtues", a step in a long process toward possible sainthood that began in 1967.

Benedict has so far not approved the decree -- which is needed for beatification, the last step before sainthood -- opting for what the Vatican has called a period of reflection.

The possible sainthood of Pius is one of several issues that have strained Catholic-Jewish relations. Benedict's decision to readmit to the Church a bishop who denied the extent of the Holocaust in January also strained ties.

Richard Williamson had said in an interview he believed there were no gas chambers and that no more than 300,000 Jews perished in Nazi concentration camps, rather than the 6 million accepted by most historians.