"They were being rushed by some very tough people and they used tear gas", Trump said Monday of the previous day's encounter.
United States officials on Sunday reopened the crossing at the San Ysidro port of entry between San Diego and Tijuana, the most heavily trafficked land border in the Western Hemisphere after shutting it down for several hours.
The migrants involved in Sunday's incident were a fraction of a caravan of more than 5,000 that is now stuck in limbo in Tijuana.
To enter the U.S. legally, migrants must apply for asylum, but the wait for those requests to be processed can last up to a year.
After the violence, Lurbin Sarmiento of Honduras walked back to the sports center with her four-year-old daughter.
Nielsen said her agency was prepared to address any future violence by deploying more USA military forces.
"We ran, but the smoke always reached us and my daughter was choking", Sarmiento said, visibly shaken.
She said she never would have gotten that close with her daughter if she thought there would be tear gas.
Wind carried the gas beyond the migrants who charged the fence and took it toward people waiting some distance away, APTN reported.
Sunday's melee closed one of the world's busiest global crossings, San Ysidro Port of Entry, near San Diego, to vehicle and pedestrian traffic for several hours.
U.S. tourist killed by Indian tribe in Andaman islands, 7 held
Incidentally, the island is inhabited by the Sentinelese who refuse to connect with the rest of the world. The tribal people reportedly fired arrows at helicopters sent to retrieve the bodies.
On Friday, Tijuana Mayor Juan Manuel Gastelum declared a humanitarian crisis in his city, which is home to 1.6 million people.
Irineo Mujica has traveled with the migrants for weeks as a representative of the aid group Pueblo Sin Fronteras. "Far from helping the caravan, they are hurting it", he said in an interview with broadcaster Milenio.
He said that according to CBP's initial report, 69 people were apprehended entering the US.
Brandon Judd, president of the National Border Patrol Council, said border agents' use of tear gas on caravan migrants trying to breach the U.S. -Mexico border was the "appropriate level of action". He also made new arguments for his promised border wall.
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.
"Do it by plane, do it by bus, do it any way you want, but they are NOT coming into the United States of America", the president, who spent his Thanksgiving break with his family at his Mar-a-Lago resort in Palm Beach, Florida said.
But one Honduran man, who did not give his name, told AFP American officers had "got upset because we were close to the border". Democrats and even some lawmakers in Trump's own party have resisted his calls to fund his proposed border wall.
Trump has repeatedly suggested without evidence that the group of migrants is filled with criminals. According to the AP, officials are now processing fewer than 100 asylum applications per day.
An estimated 8,200 migrants from the so-called caravans heading to the U.S. from Central America are now in Mexico, authorities say. George Grow was the editor.
Republican US Senator Joni Ernst told CNN she did not want a government shutdown but that "we're seeing results" from Mr Trump's efforts on asylum seekers.
In a diplomatic memo to theUS Embassy in Mexico City on Monday, the Ministry of Foreign Relations requested an "exhaustive investigation" into the use of non-lethal weapons by the United States toward Mexico, the ministry said in a statement.