A row has flared over Pope Benedict XVI's membership as a teenager of the Hitler Youth, as he paid a historic visit to Jerusalem's holy sites, BBC reported.
A Vatican spokesman said the pontiff had "never, never, never" belonged - contradicting the Pope's own admission.
The comments came as he visited the Dome of the Rock - the first pontiff to do so - and then the Western Wall, one of Judaism's holiest places.
Pope Benedict then said Mass for thousands in the Josaphat valley.
It is the second day of his five-day visit to Israel and the Palestinian territories.
Vatican spokesman Rev Federico Lombardi said: "The Pope was never in the Hitler Youth, never, never, never."
But his remark appeared to contradict the Pope's own words in his 1997 memoirs, Salt of the Earth.
"As a seminarian, I was registered in the HY [Hitler Youth]," he said then. "As soon as I was out of the seminary, I never went back."
The Rev Lombardi sought to make a distinction between the anti-aircraft auxiliary corps the Pope was enrolled in towards the end of the war and the
Hitler Youth, which he described as a "corps of volunteers, fanatically, ideologically for the Nazis".
For a controversy which had been puttering to an end, the Vatican appears to have fanned it energetically back into life, says the BBC's Tim Franks in Jerusalem.
There has already been criticism from Israeli politicians and commentators, who said that in his speech on Monday the Pope failed to express enough remorse for the Holocaust.
The row came as Pope Benedict visited sites in Jerusalem holy to Muslims, Jews and Christians.
He went first to the Dome of the Rock, located on the Temple Mount - a site sacred to all three monotheistic religions, and met the Grand Mufti of Jerusalem, Mohammed Mohammad Hussein.
Then the Pope followed Jewish tradition at the Western Wall, inserting a written prayer in the cracks between the 2,000-year-old stones.
He emphasised the ties that bind Christianity with Islam, and with Judaism.
"Today I have the opportunity to repeat that the Catholic Church is irrevocably committed to...a genuine and lasting reconciliation between Christians and Jews," he said.
Later at a Mass in the Josaphat Valley, he said it was a "tragic reality" that many Christians had left the region.
"In the Holy Land there is room for everyone," he said, prompting applause from the congregation.
Israel has beefed up security for the trip in an operation named "White Robe", with tens of thousands of law-enforcement officers deployed and entire sections of Jerusalem shut down.
The pontiff will later visit the site reputed to be where Jesus took his Last Supper before his crucifixion and resurrection.
