Washington DC - President Donald Trump told major pharmaceutical firms Thursday to lower prices or face punishment, as he moved to give Americans relief from medicine costs much higher than elsewhere in the world.

In letters to 17 drug companies published on Truth Social, Trump said he wants the firms to work with his administration to institute a series of changes within 60 days.

"If you refuse to step up, we will deploy every tool in our arsenal to protect American families from continued abusive drug pricing practices," Trump wrote, without specifying what the consequences would entail.

Trump is following up on an executive order he signed in May to address US drug prices that are among the highest in the world – more than three times what people in similarly developed countries pay, the White House said Thursday.

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In the letters, Trump said the response he has received so far to his order from companies has been "more of the same: shifting blame" and policy changes that would in fact benefit the industry, not consumers.

Key to the Trump plan is a "Most Favored Nation" policy that pins the cost of drugs sold in the US to the lowest price paid by other countries for the same drug.

Trump said Thursday he wants the companies to extend this pricing policy to medications used by older people under the government-backed health program Medicaid.

He also wants this status to apply to new drugs, Trump said in the letters.

"Americans are demanding lower drug prices and they need them today," Trump wrote.