Image copyright FBI

The FBI has broken up several sex trafficking rings across the US, uncovering more than 100 sexually exploited teenagers in a nationwide operation.

Agents arrested more than 150 people on sex-trafficking charges in dozens of cities including Atlanta, Denver and Seattle.

The youngest victim found was 12 years old, the FBI said.

The FBI targeted hotels, casinos and lorry stops to find under-age victims.

The majority of the teens found were girls. Agents also found three boys and three transgender teens.

The FBI worked with local police departments and the National Center for Missing and Exploited Children to help the teenage victims to find shelter and get medical attention.

The agencies want to ensure the teenagers do not return to prostitution.

"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.

The raids involved about 500 local police departments from across the country. A similar FBI-led campaign carried out last year uncovered about 160 teenagers working as prostitutes.

'Epidemic' of US children sold for sex