An international law expert says Donald Trump is walking a fine line with his latest tweets, directed at the people of Iran.

Anti-government riots have continued for a second day in Iran's capital, with protestors demanding the resignation of senior leaders after the Iranian government admitted to downing a Ukranian plane with a missile which killed all 176 passengers.

The US President has made a series of tweets in Farsi, the Persian language widely spoken in Iran, declaring support for the anti-government protestors.

Translated, his statement reads: “To the brave and suffering Iranian people: I have stood with you since the beginning of my presidency and my government will continue to stand with you. We are following your protests closely. Your courage is inspiring."

به مردم شجاع و رنج کشیده ایران: من از ابتدای دوره ریاست جمهوریم با شما ایستاده‌ام و دولت من همچنان با شما خواهد ایستاد. ما اعتراضات شما را از نزدیک دنبال می کنیم. شجاعت شما الهام بخش است.

— Donald J. Trump (@realDonaldTrump) January 11, 2020

Waikato University International Humanitarian Law Professor Al Gillespie told Tim Dower Trump's rhetoric must be carefully worded.

"He can't be seen to be pushing too hard because that's not only illegal in international law, it's also going to be counter-productive to what he wants."

He believes that the Iranian government should pay-up for its mistake. Gillespie says the government may use procedures from similar events such as the Lockerbie bombing.

"Best practice in these types of matter, once there is proof or admission of guilty, the country moves towards giving some kind of recompense towards the tragedy that occurred."