Donald Trump called for a special prosecutor to investigate Hillary Clinton's tenure as secretary of state, as questions emerge over whether foreign donations to the non-profit Clinton Foundation influenced her decision-making while in office, NBC News reported Tuesday.

The GOP nominee demanded an "expedited investigation by a special prosecutor" into Clinton's ties to the Clinton Foundation during her time at the State Department. 

"The Clintons made the State Department into the same kind of pay-to-play operation as the Arkansas government was," Trump said.

The comment was Trump's first explicit call for direct legal action against his Democratic rival beyond his common stump-speech claim that Clinton should be jailed for her use of a private email server while US secretary of state. 

The US Justice Department declined to bring charges against Clinton over her email server. 

Clinton's campaign would not directly address Trump's comments.

A statement from campaign chairman John Podesta defended the Clinton Foundation's plans to stop accepting foreign donations and for former President Bill Clinton to step down if Clinton is elected. 

Podesta again called on Trump to release his tax returns and to divest himself of potential conflicts of interest "to ensure that he is not letting his own financial interests affect decisions made by his potential administration."

Source: MENA