Washington, July 25 -- US President Donald Trump has threatened to impose tariffs on Mexico over concerns regarding lettuce following a foodborne illness outbreak, and on Canada over wildfire smoke drifting into the US, expanding his reliance on trade threats beyond conventional economic matters.

Speaking to reporters in the Oval Office following an event focused on nuclear energy on Friday, Trump was asked if it was "safe to eat lettuce again" amid an escalating foodborne illness outbreak.

"I think we'll put a major tariff on Mexico because of the lettuce. And we'll put a big tariff on Canada because of the smoke," Trump said.

The US President made these comments while American health authorities investigated a countrywide cyclosporia...