Openlands Lakeshore Beach. | Photo: Ignas Vlog (Google Maps).

Police and the bomb squad recovered explosive materials near a shoreline at a Highland Park forest preserve twice this week, officials said, adding that they are working with the military on the situation.

The Highland Park Police Department responded first on Tuesday to the Openlands Lakeshore Preserve, 3136 Patten Road, for a report of explosive materials found.

The City of Highland Park said in a statement that the Waukegan Bomb Squad responded to assist Highland Park police with the situation.

The explosives were found on the shoreline of the lakeshore preserve at the bottom of the bluff, according to the Openlands Lakeshore Preserve.

The explosives were removed in a “safe and secure manner,” city officials said.

Police responded back to the same area again later in the week after additional explosives material was located.

The entire Openlands Lakeshore Preserve has been closed to the public until further notice as an investigation is conducted.

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Openlands said they are working with the military and all persons must keep off the bluff and lakefront until the investigation is complete.

Authorities did not say what kind of explosives were found or how long they may have been there.