WARSAW (REUTERS).- Poland is offering a reward for the return of the German-language sign "Arbeit macht frei" ("Work makes you free"), whose theft from the former Nazi Auschwitz death camp has shocked many Poles.

The Prime Minister's office also has ordered an investigation, the PAP news agency said on Saturday.

The reward of 115,000 zlotys (about $39,000) is being offered by the Auschwitz museum, police and anonymous donors for information leading to the return of the metal sign which hung over the entrance to the death camp, PAP said.

"I am shocked and outraged by the theft of a recognizable symbol of Nazi cynicism and cruelty," President Lech Kaczynski said in a statement.

"Everything must be done to find and punish the offenders... and I appeal to all my compatriots who can help the law-enforcement authorities."

The sign, intended to delude Jews and others who were brought to the camp to be gassed to death into thinking they were entering a work camp, was stolen on Friday, sparking an international outcry and soul-searching within Poland.

Some 1.5 million people, most of them Jews, died at the camp during World War Two as part of Nazi Germany's extermination program, and Auschwitz has come to symbolize the Holocaust in which six million Jews perished.

Following talks with Israeli President Shimon Peres at the Copenhagen climate conference, Prime Minister Donald Tusk told TVN24: "Clearing up this matter is a top priority. I am sure those responsible will soon be caught."

His aide Tomasz Arabski told PAP that Tusk had ordered the interior minister to mount a major investigation into the theft.

Jaroslaw Gowin, a leading lawmaker of the ruling Civic Platform party, said he thought the theft was meant to disgrace Poland internationally.

"I think that behind this theft was cold calculation designed to entrench the view that anti-Semitism is widespread in Poland," he told news channel TVN24.

Szewach Weiss, Israel's former ambassador to Poland, called the theft "a disgraceful act" but added: "I do not blame the Polish nation for it."

Provincial police spokesman Dariusz Nowak told Reuters by telephone that four museum guards had been questioned but there were no leads in the theft of the sign from the former camp, now a museum, in the southern Polish town of Oswiecim, near Krakow.

"There has been no breakthrough in the case, but the investigation is being vigorously pursued," Nowak said.

He said the gate from which the sign was removed was not directly monitored by closed-circuit cameras.

Museum director Jasroslaw Mensflet has said the site's security system is undergoing modernization, but the project has not been completed.

"On the site of the former Auschwitz camp a global fiber-optic system is being developed, and part of it is already in place. The system will combine the Internet, visual monitoring, motion sensors and a modern fire-alarm system," he told PAP.

(Reporting and writing by Rob Strybel; Editing by Michael Roddy)