Police in South Los Angeles are trying to figure out why someone left a pair of old military grenades in the backyard fire pit of a house.

The new owner of a home in the 400-block of 70th Street was doing some cleaning and happened upon the rusted explosives, said Omar Bazulto, the watch commander at the Los Angeles Police Department's Newton Division.

The pins, which trigger grenades to blow up, were still intact.

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Officers evacuated a 300-foot area around the house shortly after noon on Sunday, when the explosives were discovered.

It was not immediately clear how old the grenades were, of if the ammunition inside was still live.

The department's bomb squad planned to detonate the grenades on site on Sunday.