Children as young as 12 were rescued from sex trafficking rings across the US as part of a nationwide sting by the FBI. Agents arrested more than 150 people on sex trafficking charges in cities including Atlanta, Denver and Seattle.

The agency said that 149 children were rescued in Operation Cross Country, which was conducted alongside local police forces and the National Center for Missing and Exploited Children.

The FBI targeted hotels, casinos and lorry stops to find underage victims of sexual exploitation. The majority of those rescued were girls. Agents also found three boys as well as transgendered teens.

"When kids are treated as a commodity in seedy hotels and on dark roadsides, we must rescue them from their nightmare and severely punish those responsible for that horror," FBI director James Comey said in a statement.

A similar FBI campaign last year found 160 teenagers working as prostitutes.

"As these recoveries are coming in during the operation, we're all ecstatic because we're saying, 'Great they're finding more and more kids.' But it's also mixed feelings because we wish, quite frankly, that this was an operation that didn't have to occur," said Angela Aufmuth of the National Center for Missing & Exploited Children.