For a second straight day, President Donald Trump on Friday threatened to close the southern U.S. border with Mexico, demanding that Mexican authorities do more to stop a growing tide of illegal immigration into the United States.

In a series of posts on Twitter, the President echoed comments he made at a campaign rally Thursday night in Michigan, where he chastised the Mexican government over immigration.

"If they don't - and I'm telling you right now - I will close the damn border," the President said to cheers in Grand Rapids, Michigan.

“I will be CLOSING.....the Border, or large sections of the Border, next week,” President Trump tweeted.

It wasn't immediately clear what parts of the border, what border crossings might be involved, or how it would impact trade between the U.S. and Mexico.