Autism diagnoses in the US have increased significantly since 2000, intensifying public concern.
By 2020, the US autism rate in eight-year-olds was 1 in 36, or 2.77 per cent, up from 2.27 per cent in 2018 and 0.66 per cent in 2000, according to the US Centers for Disease Control and Prevention.
"At your direction, we are going to know by September. We've launched a massive testing and research effort that's going to involve hundreds of scientists from around the world," Kennedy said at a meeting of US President Donald Trump's cabinet.
"By September, we will know what has caused the autism epidemic and we'll be able to eliminate those exposures."
Trump in February ordered the creation of a "Make America Healthy Again" commission made up of Kennedy and other secretaries to look at everything from the rates of autism and asthma in children to how much medicine is being prescribed to them for ADHD or other conditions.
"There's got to be something artificial out there that's doing this," Trump told Kennedy at the meeting.
"There will be no bigger news conference than when you come up with that answer."
Scientists have been researching for decades what genetic or environmental factors might contribute to autism but the causes of most cases remain unclear.
They say that the major drivers of the increase in US autism rates are an expanded definition that includes more types of behaviours and more widespread awareness and diagnosis.
There may be multiple studies already underway on autism, a neurodevelopmental condition that affects how a person's brain functions.
Kennedy has in the past questioned if routine childhood vaccines may be linked to autism.
The belief first gained traction decades ago after the publication of flawed studies that have since been retracted.
Decades' worth of subsequent studies have found no connection between vaccines and autism.
with AP
