A report in The Wall Street Journal cited people in Washington who are familiar with the matter as saying they were encouraged by recent developments around Assange who has been taking refuge in Ecuador's London embassy since June 2012.
It said over the last year, US officials had discussed various charges that could be levelled against Assange.
The WikiLeaks publisher had had restrictions on his Internet and telephone use placed on him by Ecuador and filed a case against it which he lost. His lawyers are appealing the verdict.
Assange has said that he fears being extradited to the US if he leaves the embassy in London. Last year, US officials said arresting him was a top priority.
The WSJ report said there had been thought given to publicly indicting Assange in order to provide Ecuador with a reason to evict him from the London embassy.
The charges were not specified but the sources involved said they could include the US Espionage Act.
Assange's problems began when he visited Sweden in August 2010 to attend a conference where he was scheduled to give a talk. During that visit, he had sex with two women whom he met. The pair filed rape and molestation complaints against him later, claims that he denied.
He was questioned by Swedish authorities and cleared. He could have left the country then and there, but stayed for a while, in case the authorities decided to question him again.
Interpol issued a Red Notice for his arrest on 20 November 2010. On 27 November, Assange surrendered to authorities and appeared before a Westminster judge. He was granted bail in December after his backers provided £240,000 in cash and sureties.
A legal back and forth eventuated and went on until June 2012, when Swedish prosecutors sought his extradition.
Assange's lawyers, among them the world-renowned Australian Geoffrey Robertson, replied that if he agreed to the extradition request, then he could be flown to the US from there.
On 19 June 2012, he jumped bail and took refuge in the Ecuadorian embassy, seeking asylum in the South American country. British police surrounded the building and blocked any chance of his leaving.
Ecuador granted him asylum in August 2012. He has had to stay inside the four walls of the embassy since then. He was granted Ecuadorian citizenship by a former president of the country, Rafael Correa.