Actor and human rights campaigner Ashton Kutcher has urged US lawmakers to support efforts to help bring an end to child sexual exploitation.

At a senate hearing on Wednesday, a visibly emotional Mr Kutcher said it was time for "society and government" to defend the vulnerable.

He said that he had been exposed to things "no person should ever see".

Mr Kutcher was speaking as chairman of Thorn, an organisation that develops software to locate victims of abuse.

"The right to pursue happiness for so many is stripped away, it's raped, it's abused, it's taken by force," Mr Kutcher, 39, said.

He told the US Senate Foreign Relations Committee in Washington that new technology was needed to prevent websites from carrying adverts promoting the sexual exploitation of minors.

"Technology can be used to enable slavery, but it can also be used to disable slavery," Mr Kutcher said, adding: "Can we build the tools that are better than their tools to fight what is happening?"

He said that one of the tools his organisation had created, Spotlight, helped identify 6,000 victims in six months. It was developed after a 2012 survey found that 63% of underage victims were being bought or sold online.

Mr Kutcher, who is married to actress Mila Kunis and has two children, said that he aimed to help victims around the world with his work at Thorn after being affected by what he had seen.

"I've seen video content of a child that's the same age as mine, being raped by an American man who was a sex tourist in Cambodia. This child was so conditioned by her environment that she thought she was engaging in play."

He told those present at the Ending Modern Slavery hearing that his organisation had been approached by authorities to help track online perpetrators with new technology.

"We were the last line of defence - an actor and his foundation," he said, adding: "That's my day job, and I'm sticking to it."