Over the weekend, violent clashes occurred as the United States attempted to stem the flow of people crossing into the country.
The San Ysidro Port of Entry at the US-Mexico border was closed for several hours on Sunday after Customs and Border Protection (CBP) agents opted to deploy tear gas in an effort to disperse migrants wanting to gain entry.
Like other federal law enforcement officers, Border Patrol agents are allowed to use force if they think they are under attack.
Mr McAleenan added: "As the events unfolded, quick, decisive and effective action prevented an extremely risky situation".
As a result, numerous Central American migrants who tried to rush the border were tear gassed.
Many users on social media debated whether tear gas is a chemical weapon, and if it is, why was it used against migrants? But Sunday's action affected only the San Ysidro crossing and the USA forces appeared limited to Customs and Border Protection officers and Department of Homeland Security police, backed by San Diego police and the California Highway Patrol.
Chief Patrol Agent Rodney Scott told CNN "numerous" people had made it across the border on Sunday, adding that most of those who were detained were men.
US Homeland Security Secretary Kirstjen Nielsen accused the migrants of seeking to harm US border patrol personnel "by throwing projectiles at them".
Image A migrant family runs from tear gas released by US border patrol
One of the migrants at a temporary shelter in Tijuana, Mexico.
About 5,000 Central American migrants have been staying at a sports center in Tijuana for more than a week. Pictured in a now-viral image is a mother sprinting away from the tear gas bombs, with two young, barefooted children in hand.
"Mexico should move the flag-waving Migrants, many of whom are stone cold criminals, back to their countries", Trump said in an early morning tweet.
So far, around 2,400 members of the migrant caravan have reached the U.S. -Mexico border, and a thousand more are expected this week.
Mexico's National Institute of Migration Commissioner Gerardo Garcia confirmed the 98 arrests on his country's side, saying there were "instigators" in the migrant caravan pushing people to illegally cross the border.
Numerous migrants say they are fleeing violence and poverty in Honduras in search of asylum north of the border. Tear gas fumes were carried by the wind toward people who were hundreds of feet away, including some children. "Congress, fund the WALL!"
Trump wants migrants to remain in Mexico while their USA asylum cases are adjudicated.
The incident lasted almost two hours, with two groups of migrants tear gassed after they crossed the Tijuana River, eventually returning to a stadium where they've camped for days, waiting for the opportunity to apply for asylum. Under US and global law, an unauthorized crossing is not grounds to block someone from claiming asylum; neither does it change limits on the appropriate use of force.
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No visiting fans are allowed in the stadium, following a 2013 ban on away fans to stop football related violence in Argentina . Television pictures from the entrance to the Boca dressing room showed many players and staff seemingly affected by the gas.