CBP Commissioner Kevin McAleenan told reporters Monday that as many as 1,000 people that were part of a migrant caravan traveling through Central America and Mexico sought to enter the U.S. illegally.
A Central American migrant sits on top of the border structure separating Mexico, left, and the United States, right, as U.S. Border Patrol agents look on, right, Wednesday, Nov. 14, 2018, seen from Tijuana, Mexico.
The US president's threat comes a day after American authorities closed the country's busiest southern border crossing and fired tear gas into crowds.
The group was stopped by a chain-link fence topped with barbed wire and US Border Patrol agents firing tear gas and rubber bullets.
"As the events unfolded, quick, decisive and effective action prevented an extremely unsafe situation", he said.
The agency said that officers chose to use the tear gas "because of the risk to agents' safety". On the east side, some pulled back a panel of fencing made of Army surplus steel landing mats to create an opening of about 4 feet, through which a group of more than 30 people crossed, according to a USA official who was not authorized to discuss the matter publicly and spoke on condition of anonymity.
U.S. Department of Homeland Security Secretary Kirstjen Nielsen said in a statement that the agency has "confirmed that there are over 600 convicted criminals traveling with the caravan".
Mexican police had kept them from walking over a bridge leading to the Mexican port of entry, but the migrants pushed past officers to walk across the Tijuana River below the bridge.
For weeks before the 6 November congressional elections, Mr Trump raised the alarm about the migrant caravans and ordered some 5,800 USA troops to the border to support border patrol agents. "In diapers. Choking on tear gas", California Governor-elect Gavin Newsom tweeted.
Irineo Mujica, who has accompanied the migrants for weeks as part of the aid group Pueblo Sin Fronteras, said the aim of Sunday's march toward the USA border was to make the migrants' plight more visible to the governments of Mexico and the U.S.
According to Trump, Border Patrol had to utilize tear gas because hundreds of caravan riders were becoming violent and agents' lives were at risk.
Alyssa Milano, Kathy Griffin, and Rosie O'Donnell slammed President Trump after Sunday's border clash. Democrats and even some lawmakers in Trump's own party have resisted his calls to fund his proposed border wall. He said the aim of Sunday's march was to make the migrants' suffering more visible to US and Mexican officials. With a backlog of cases that number into the thousands, many migrants appear set to linger along the border for months, if not longer.
Tijuana Mayor Juan Manuel Gastelum on Friday declared a humanitarian crisis in his border city of 1.6 million, which he says is struggling to accommodate the crush of migrants.
"This policy that we use was an Obama-written policy and it was used in 2013 at the same port of entry", he told CNN, wondering in particular about the intense media interest now versus then.