Police in Germany are investigating the theft of the "Arbeit Macht Frei" sign from the main gate at Dachau concentration camp.

A section of the wrought-iron sign, measuring 191 cm by 94 cm, was taken on Sunday night.

Security guards failed to spot the thieves, who had to scale another gate to get to the sign.

The site's director, Gabriele Hammermann, condemned the thieves. She said the sign, which in English means "Work sets you free", was "the central symbol for the prisoners' ordeal".

She defended the lack of surveillance cameras at the site, saying that she didn't want to turn Dachau into a "maximum-security unit".

But she said that that decision may now have to be reconsidered.

Yad Vashem, the Holocaust memorial in Israel, said: "The theft of such a symbolic object is an offensive attack on the memory of the Holocaust."

Dachau was the Nazis' first concentration camp. Set up in 1933, more than 30,000 people were murdered there.

The crime follows a similar theft in 2009, when the "Arbeit Macht Frei" sign above the gates of Auschwitz was taken. Three men were jailed for the theft.