Donald Trump has called on Syria to release American journalist Austin Tice, who went missing in the country nearly eight years ago and is believed to have been detained by the Syrian regime.

“We have one young gentleman, Austin Tice, and we're working very hard with Syria to get him out. We hope the Syrian government will do that,” Mr Trump said at a press conference on Thursday.

“Syria, please work with us. We would appreciate you letting him out,” he added.

Mr Tice went missing in Syria in August 2012 while reporting on the country's civil war, just days before his 31st birthday. He was believed to have been captured by the Syrian government outside of Damascus, however Syrian officials have publicly denied any knowledge of his whereabouts.

"Think about what we've done. We've gotten rid of the Isis caliphate. We've done a lot for Syria," Mr Trump said in his public plea.

When asked by a reporter whether he was saying he knew Mr Tice, a former Marine veteran, was still alive, Mr Trump replied: "No, I'm not. But we're trying to find that out."