(CNN) All children in US Border Patrol custody have received medical screenings and apprehended children will now be assessed more thoroughly, Homeland Security Secretary Kirstjen Nielsen announced Wednesday in a statement on the death of an 8-year-old Guatemalan boy in Border Patrol custody.

"This tragedy, the death of a child in government custody is deeply concerning and heartbreaking," Nielsen wrote in the statement. "In the last 24 hours, I have ... directed a series of additional actions to care for those who enter our custody."

"Moving forward, all children will receive a more thorough hands on assessment at the earliest possible time post apprehension -- whether or not the accompanying adult has asked for one," Nielsen writes in the statement.

House Minority Leader Nancy Pelosi announced Wednesday that Congress will investigate border deaths of children and said Democrats want the Homeland Security Department's inspector general to investigate the death of the 8-year-old boy.

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