Donald Trump's threat of US military strikes against drug cartels inside Mexico is a non-starter, Mexican President Claudia Sheinbaum said Tuesday.

'It's not going to happen,' she said at a press conference, responding to Trump's warning that he would do 'whatever we have to do,' including strikes within the territory.

Trump on Monday told reporters in the Oval Office that he would be 'OK' with assaults on drug lords operating inside Mexico, arguing that it would be justified to stop the inflow of the deadly opioid fentanyl.