Donald Trump revealed on Tuesday that Mexico agreed to take stronger legal action to halt Central American migrants if its initial efforts to stem the flow don’t show results in 45 days.

In bright sunshine outside the White House, the US president waved what he said was the text of an agreement Mexican and US officials signed on Friday to avert the application of tariffs on their exports to the United States.

Photographs of the document revealed that Mexico appeared to pledge to enact or enforce certain domestic laws if Washington is not satisfied with the results of its first promised efforts – deploying 6,000 National Guardsmen to reinforce its southern border and expanding its policy of taking back asylum-seekers as the United States processes their claims.

If, after 45 days, the US government "determines at its discretion" that the results aren’t enough, the document says, "the Government of Mexico will take all necessary steps under domestic law to bring the agreement into force."

The document gives the Mexican government another 45 days to achieve that.