Adam Stuart Busby, 66, is charged with emailing 17 bomb threats to the University of Pittsburgh in April 2012. He was released to an Irish hospital on March 21, according to US federal prosecutor David Hickton.
Mr Busby is waiting for Ireland's Supreme Court to hear his appeal against an order extraditing him to Scotland, where he faces charges that he threatened to poison water supplies and the then Prime Minister Gordon Brown in 2010.
Mr Hickton said he was working to ensure Mr Busby is taken to the US after the UK charges are resolved. Mr Busby, originally from Paisley, faces charges in Pittsburgh including threatening a federal law enforcement officer, fraud by wire and international extortion.
Mr Hickton said: "We are monitoring the proceedings and working to obtain his extradition to the US on the charges pending here. We're resolved and committed to bring him to justice here whenever we can."