Pope Benedict XVI held Mass in Israel's Josaphat Valley, beneath the Mount of Olives
A row has flared over Pope Benedict XVI's membership as a teenager of the Hitler Youth, as he paid an historic visit to Jerusalem's holy sites.
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."
Katya Adler, BBC News, Jerusalem
The Mass in the picturesque and historically charged Josaphat Valley is not well attended.
The 5,000 tickets for the Mass were sold out. Olive trees were temporarily removed to make room for the anticipated crowds of enthusiastic pilgrims. Yet few have actually turned up.
The adoration that followed Pope Benedict's predecessor during his visit to the Holy Land nine years ago seem to be conspicuously absent.
The Middle East is also a sadder and darker place.
John Paul came here in March of the millennium year - before the 11 September attacks, before the US-led invasion of Iraq, before the second Palestinian uprising and Israel's tougher controls on Palestinians.
Ahead of Pope Benedict's visit few Christians said they believed he could or would improve their lives much. Their absence here today, if for that reason, speaks volumes.
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.
POPE IN THE MIDDLE EAST
Monday Arrives in Israel, meets President Shimon Peres
Tuesday Visits the Dome of the Rock and the Western Wall. Celebrates Holy Mass in Josaphat Valley
Wednesday Visits Bethlehem, visits refugees, meets Mahmoud Abbas
Thursday Mass in Nazareth, talks with Benjamin Netanyahu, meets Franciscans
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