More than 2,000 people have been killed during the violent crackdown by security forces on protests in Iran, a human rights group has said, as President Trump promised Iranians that help was "on its way".

The US-based Human Rights Activists News Agency (HRANA) reported that it had so far confirmed the killing of 1,850 protesters, 135 people affiliated with the government and nine uninvolved civilians as well as nine children over the last 17 days despite an internet blackout.

An Iranian official also told Reuters that 2,000 people had been killed but that "terrorists" were to blame.

He has been weighing military and other options in response to the crackdown, having already announced 25% tariffs on any country trading with Iran.

The protests, which have reportedly spread to 180 cities and towns in all 31 provinces, were sparked by anger over the collapse of the Iranian currency and soaring cost of living.

They quickly widened into demands for political change and became one of the most serious challenges to the clerical establishment since the 1979 Islamic revolution.