The infamous Arbeit Macht Frei sign at the entrance to the Auschwitz Nazi death camp in Poland has been stolen.
The wrought iron sign, whose words mean "Work Sets You Free", was unscrewed and pulled down from its position above the gate in the early hours of Friday.
Polish authorities denounced the theft, while Israel's Holocaust museum branded it an "act of war".
More than a million people - 90% of them Jews - were murdered by the Nazis at Auschwitz during World War II.
Investigators say at least two people would have been needed to steal the five-metre-long (16ft), 40kg (90lb) sign.
The theft occurred between 0330 and 0500 local time on Friday, police spokeswoman Katarzyna Padlo told AP news agency.
HISTORY OF AUSCHWITZ SIGN
Made by Polish political prisoners in 1940
Letter 'B' thought to have been reversed as act of defiance - making it appear upside-down
Locals say Red Army soldiers were bribed to leave it in Poland after camp was liberated
Occasionally replaced by replica while conservation work is done
Jarek Mensfelt, from the Auschwitz-Birkenau Museum, told the BBC: "It is more than just stealing something. It is a desecration.
"Somebody who did this must have been a person who had a knowledge of our security system because all the area is closed at night and patrolled and there is a system of cameras," he added.
"This was not an incident - this was a deliberate and organised action."
Avner Shalev, director of Israel's Yad Vashem Holocaust Memorial, said the theft "constitutes a true declaration of war".
He added: "We don't know the identity of the perpetrators but I assume they are neo-Nazis."
Polish ex-President Lech Walesa described the theft as "unthinkable", while Poland's chief rabbi said he could not imagine who would do such a thing.
"If they are pranksters, they'd have to be sick," said Michael Schudrich.
Polish President Lech Kaczynski called on the public to help recover the sign, which he described as a "worldwide symbol of the cynicism of Hitler's executioners and the martyrdom of their victims".
Israeli President Shimon Peres also condemned the theft during a special meeting with Poland's Prime Minister Donald Tusk.
In a statement, his office said Mr Peres "expressed the deepest shock of Israel's citizens and the Jewish community across the world", and urged Poland to "make every effort" it could to find the criminals and return the sign.
The BBC's Adam Easton in Warsaw says police are interviewing security guards and viewing closed circuit television footage.
It is not clear why it was stolen but museum officials say the widely recognised sign would be difficult to sell.
Oswiecim Police spokeswoman Malgorzata Jurecka told AFP: "All leads are being considered, but we are focusing on a theft ordered by a private collector or a group of individuals."
It is the first time the sign, made by Polish prisoners, has been stolen since it was erected in 1940.
It has now been replaced with a replica while the hunt continues.
A 5,000-zloty ($1,700; £1,050) reward has been offered for information leading to the capture of the thieves, reports AP.
The cynical slogan "Arbeit Macht Frei" was also used at the entrances to other Nazi camps, including Dachau and Sachsenhausen, although the one at Auschwitz is perhaps the best known.
Hundreds of thousands of prisoners passed under the sign into the camp during the Holocaust, but the majority were murdered or worked to death.
The theft comes just days after the German government pledged 60m euros ($86m) to an endowment fund to help preserve the camp.
Auschwitz, which receives more than a million visitors a year, has been run as a state museum since 1947.
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