(CNN) Philadelphia police are investigating last week's death of H.R. McMaster's father as "suspicious," the department told CNN on Thursday.

H.R. McMaster Sr., the father of the military general and former national security adviser to President Donald Trump, died last Friday of blunt impact head trauma, according to the Philadelphia Department of Health. His death was ruled an accident, said James Garrow, a department spokesman.

Police didn't elaborate on why his death is being treated as suspicious.

The elder McMaster was a resident at Cathedral Village, a continuing care retirement facility in Philadelphia.

H.R. McMaster Sr., the father of Gen. H.R. McMaster, died on April 13 at Cathedral Village in Philadelphia.

The Pennsylvania attorney general's office is working with the Philadelphia police to "thoroughly and carefully review this tragic incident," said Joe Grace, spokesman for Attorney General Josh Shapiro. The investigation is in its "very early" stages, according to Grace.

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