The assurance is part of an ongoing effort to put Assange on trial for espionage and computer fraud. The US has been after Assange ever since Wikileaks published thousands of secret files and classified information that shed light on war crimes committed by US troops in Iraq and Afghanistan.
Earlier on Wednesday, the US received limited permission from a UK court to appeal a January decision not to extradite Assange. The court blocked the extradition citing health concerns and suicide risk should he be placed in the US prison system.
The US has also reportedly assured Assange that he can serve any jail time in his native Australia should he be tried and convicted.
Assange’s fiancée, Stella Moris, urged the US government on Wednesday to drop its extradition case against him and put an end to his "purgatory" in a UK prison. She also noted that the case against Assange is falling apart after one of the key witness for the prosecution had recently admitted that he lied in the indictment in exchange for immunity from US prosecutors.
In January, UK district judge Vanessa Baraitser ruled not to extradite Assange to the United States, citing health reasons and the risk of suicide in the US prison system, but decided that he must wait in prison for the outcome of the appeal by US prosecutors.