Donald Trump has made a Thanksgiving Day threat to close the US border with Mexico and says troops can use lethal force against migrants "if they have to".
The US president said he had given the thousands of active duty troops he sent to the border the "OK" to use lethal force against migrants if Mexico "lost control" on their side.
Thousands of migrants have been fleeing Central America to get to the border, and the president sent almost 6,000 troops there earlier this month.
Mr Trump, who did not say how long the border would be closed, also hinted at the possibility of a partial government shutdown early in December over the refusal by courts to allocate the billions of dollars he is demanding for a border wall – a central plank of his presidential campaign in 2016.
He said: "Could there be a shutdown? There certainly could, and it will be about border security, of which the wall is a part."
The president's comments came in a wide-ranging press conference at his Florida golf club after he conveyed holiday wishes in a telephone call with members of the American military serving around the globe.
The president expressed his gratitude for their commitment to protecting the country and its interests.
Mr Trump's border threat comes days after a federal judge put the president's administration's asylum policy on hold.
Under that new policy, Mr Trump declared nobody could apply for asylum except at an official border entry point.
Some ports of entry are already facing huge queues with people having to wait for weeks.
The government shut down one port of entry, San Ysidro, in California, for several hours early on Monday morning to boost security amid concerns about a potential influx of migrant caravan members.
Most of the lanes were reopened before the morning rush hour.
Mr Trump claimed there were "fistfights all over the streets" in Tijuana, Mexico, which the migrants have reached, and "these are not like normal, innocent people".
He went on: "These are people you talk to them and they start a fistfight. I don't want that in this country."
He said the people of Tijuana "opened up with wide arms" to welcome the caravan of immigrants trying to reach the border and "now they're going crazy to get them out … because bad things are happening".
More from Donald Trump
Mr Trump vowed to close the entire border if US officials "find that it gets to a level where we are going to lose control or where people are going to start getting hurt".
Mexico would be hit economically as it would not be able to ship cars into the US, the president added.