US President Donald Trump said to the press that Iran would be "hit very hard" if more protesters die during demonstrations triggered by the economic protests that entered a second week.

"We're watching it very closely. If they start killing people like they have in the past, I think they're going to get hit very hard by the United States," Trump said aboard Air Force One on January 5.

At least 20 deaths have been reported by human rights groups in protests that began a week ago, when the Iranian rial fell to a record low against the US dollar.

Authorities have attempted a dual approach to the protests, acknowledging the economic crisis and offering dialogue with demonstrators while meeting more forceful displays of dissent with violence.

The protests began among traders and shopkeepers in Tehran before spreading to universities in the capital, then to provincial cities, where protesters have been chanting against Iran's clerical rulers. They are the largest demonstrations the country has experienced in the past three years.

Trump had on January 2 threatened to intervene if Iran suppressed protests, prompting Tehran to threaten US troops. The latest threats come after the US captured Venezuela's Nicolas Maduro, an ally of Tehran, prompting concerns that Trump may attempt regime change elsewhere.

Israeli Prime Minister Benjamin Netanyahu expressed solidarity with protesters while opposition leader Yair Lapid said the "regime in Iran should pay close attention to what is happening in Venezuela."

On Venezuela, Trump said the country was "a dead country, we have to bring it back," adding that oil companies would go back into the country and invest in the infrastructure, which has suffered from years of neglect due to sanctions. 

He added that the "country was a mess," he added that the US government is not going to invest in the country but would rely on the private sector.