US President Donald Trump on Saturday weighed in on protests in Iran for a second straight day, warning that the country’s people want change and "oppressive regimes cannot endure forever."

Trump posted on Twitter two clips of his speech to the UN General Assembly in September in which he took aim at the Iranian regime, which Washington has held out as its top adversary in the Middle East.

"Oppressive regimes cannot endure forever, and the day will come when the Iranian people will face a choice," he tweeted, quoting from the speech.

"The world is watching!"