text: Paul Charles Wilkins, 70, of Littleport, Cambridgeshire, travelled to California in January to "engage in illicit sexual conduct" with boys aged 10 and 12, US officials said.
  He initially denied four charges but later admitted transporting the images.
  Under a plea agreement he is expected to be sentenced to 13 years in January.
  He was jailed for 56 months in the UK in 2011 for possessing indecent images of children.
  More on this and other news from Cambridgeshire
  Wilkins, who holds dual UK and US citizenship, was on probation when he left the UK on 31 January.
  He set up an online site enabling him to arrange to meet boys, but was caught in a sting operation in Palm Springs, California, by undercover Homeland Security Department special agents.
  He had paid one agent $250 (Â£170) to have sex with a nine-year-old Mexican boy.
  Wilkins had initially denied four charges of travelling with the intent to engage in illicit sexual conduct, attempted sex trafficking of children, transportation of child pornography and possession of child pornography, the US District Attorney's Office said.
  A trial date was set for November, however, at a hearing on Wednesday he pleaded guilty to transporting child pornography under a plea agreement with the US Attorney's Office.
  He agreed to a 13-year prison term and a lifetime of supervised release, the US Department of Homeland Security said.
  Wilkins also admitted in court to travelling to the US in order to have sex with two young brothers, paying to have sex with the nine-year-old, possessing pornography and bringing a computer into the US containing "graphic images of boys ranging in age from five to eight".
  US Attorney Eileen Decker, chief federal law enforcement officer in the Central District of California, described Wilkins as a "predator" and "extremely dangerous".
  The plea agreement meant he would "be in prison for well over a decade," she said.
  As part of the agreement the three other counts are expected to be dismissed when Wilkins is sentenced for the transportation charge.
  Wilkins was detained as part of Homeland Security's Operation Predator, an international initiative to protect children from sexual predators.
target: A convicted British sex offender caught trying to pay US undercover officers for sex with a boy has admitted taking pornographic images into the country.