Barack Obama became the first sitting US president to visit a federal prison on Thursday, amid a push to reform America's expensive and overcrowded correctional system.
Obama arrived at El Reno Federal Correctional Institution in Oklahoma, where he is to meet officials and inmates and speak about proposed reforms.
Nearly a quarter of the world's prison population is concentrated in American jails. The United States accounts for less than five percent of the world's population.
Obama wants to cut the number of people incarcerated, as well as curbing the use of solitary confinement and ending mandatory minimum sentences.
"Our criminal justice system isn't as smart as it should be," he said this week, after commuting the sentences of 46 non-violent drug offenders.
"It's not keeping us as safe as it should be. It is not as fair as it should be. Mass incarceration makes our country worse off."
The United States jails as many people as the top 35 European nations combined, with African-Americans and Latinos disproportionately put behind bars.
Black and Latino Americans represent 60 percent of the prison population while only around 30 percent of prisoners are white.
The US prison system has seen an explosion in costs. At $80 billion, the budget for prisons represents a third of the Department of Justice's annual spending.