Police launched an investigation Tuesday morning after a bag containing dozens of Islamic State flags was found in an industrial area in Nazareth Illit by a municipal worker.

Police said the bag contained some 25 small flags, with holders to attach them to cars, belonging to the outlawed extremist group.

A team of city gardeners discovered the bag hidden between some bushes and reported it to the police, who opened a probe, police said in a statement.

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Nazareth Illit Mayor Alex Gadalkin said he was disturbed by the bag’s discovery, the Ynet news outlet reported.

“When something like this is discovered in the heart of a Jewish city, it needs to light up many warning signs,” he said.

Possession of materials from a designated terror organization, such as the Islamic State, is illegal under Israeli law. The group was officially declared a terror organization by Defense Minister Moshe Ya’alon earlier this year, giving officials wider tools to prosecute suspected members.

Built as a development neighborhood for Jewish immigrants next to the Arab city of Nazareth, Nazareth Illit, or upper Nazareth, has been the site of ethnic tensions in the past.

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The city’s former mayor Shimon Gafsou, currently suspended amid a graft probe, made headlines in 2013 after remarking that the city would not allow mosques or Arab schools.

The discovery of the flags comes as Israeli officials, along with European governments, have become increasingly concerned about citizens traveling abroad to join Islamic State fighters in Syria or Iraq, where thousands of foreigners are believed to have joined the jihadist organization.

באזור התעשייה בנצרת עילית נמצאו ע"י עובדי עירייה כ-25 דגלונים לרכב של ארגון דאעש. משטרת נצרת עילית פתחה בחקירה pic.twitter.com/EFTfFXSGvC — משטרת ישראל (@IL_police) October 7, 2014

On Sunday, an Israeli schoolteacher arrested two weeks ago on suspicion of “being associated with the Islamic State,” was released by the Hadera Magistrate’s Court from detention to house arrest.

Salah a-Din Mohammad, 24, is to be under house arrest for one week under “restrictive conditions” while the investigation against him continues in Israel and in Jordan, where he is believed to have acquired propaganda materials originating with the Islamic State, Channel 10 reported.

Police said on September 29 that they had arrested Mohammed, a teacher of Islamic studies at a high school in Kafr Kanna, a predominantly Israeli-Arab town in the Galilee. A search of his house revealed books, documents and files relating to banned terror organizations, including an Islamic State flag, officials said.

In early September, an Israeli citizen was found guilty of traveling to an enemy country and joining Islamic State during a four-month stay in Syria earlier this year.

Some 10 Arab citizens of Israel have left the country to join the Islamic State, a Shin Bet security service source was quoted by the Israel Hayom newspaper as saying in September. An additional number are believed to have traveled to join more moderate rebel groups such as the Free Syrian Army. Several Israeli Arabs have reportedly been killed in Syria.

In August, a picture surfaced of what appeared to be an Islamic State flag being waved at a rally on the Temple Mount in Jerusalem, raising some alarms.