President Donald Trump again threatened on Wednesday to close the U.S. border with Mexico, this time calling on Congress to take steps immediately to deal with immigration and security loopholes that he says are creating a national emergency.

"Congress must get together and immediately eliminate the loopholes at the Border!" Trump wrote in a Twitter post. "If no action, Border, or large sections of Border, will close. This is a National Emergency!"

Trump has repeatedly threatened to close the border to stem what he calls a tide of illegal immigration. On Friday, he said he would close the border this week unless Mexico took steps to stop illegal migration.