The United States is preparing charges against WikiLeaks founder Julian Assange, CNN reports.

Prosecutors had struggled to determine whether the First Amendment protected the Australian from prosecution but had now found a way to move forward, the officials familiar with the matter said on Thursday.

The US has been investigating Assange and WikiLeaks since 2010 when the whistleblower website posted thousands of pages of classified material stolen by US Army intelligence analyst Chelsea Manning.

Manning was later jailed for her role in the affair though former US president Barack Obama commuted her 35-year sentence in January and she is due to be released in May.

Assange has been holed up in the Ecuadorian embassy in London since June 2012, to prevent his extradition to Sweden where he is wanted for questioning on charges of sexual assault.

He says he is afraid he could be further extradited to the US if he is taken to Sweden.

In response to Thursday’s report WikiLeaks reposted on Twitter an opinion piece written by Assange and published in the Washington Post earlier this month.

“WikiLeaks’ sole interest is expressing constitutionally protected truths, which I remain convinced is the cornerstone of the United States’ remarkable liberty, success and greatness,” Assange wrote.

— DPA