United States President Donald Trump said on Tuesday that the US would respond forcefully if Iranian authorities began hanging people as part of their crackdown on a popular uprising.

“We will take very strong action if they do such a thing,” Trump told CBS News in an interview, when asked about reports that hangings could begin on Wednesday. “When they start killing thousands of people — and now you’re telling me about hanging — we’ll see how that works out for them,” he said in a video clip released online.

The interview took place while Trump was visiting a manufacturing plant in the northern US state of Michigan, where he also delivered a speech on the economy.

In that speech, he repeated a message he had earlier posted on social media, saying that “help is on its way” for Iranian protesters.

He said the true death toll in Iran remained unclear.

“I hear numbers — look, one death is too much — but I hear much lower numbers, and then I hear much higher numbers,” he said.

Later, speaking to reporters as he returned to Washington, Trump said he was due to receive a briefing on Iran.

“The killing looks significant, but we don’t know for certain yet. I’ll know within 20 minutes — and we’ll act accordingly,” he said.

Trump had previously said the United States would become involved if protesters were killed, a threshold that was crossed several days ago.

At least 734 people have been confirmed killed, although the real figure is likely to be in the thousands, according to Norway-based NGO Iran Human Rights (IHR).

Concerns have also increased that the Islamic republic could use the death penalty to suppress the protests, after prosecutors in Tehran said authorities would pursue capital charges of moharebeh, or “waging war against God”, against some people arrested during recent demonstrations.

“Concerns are mounting that authorities will once again resort to swift trials and arbitrary executions to crush and deter dissent,” Amnesty International said. IHR highlighted the case of Erfan Soltani, 26, who was arrested last week in the Tehran satellite city of Karaj and who, according to a family source, has already received a death sentence and could face execution as early as Wednesday.