U.S. authorities have stopped all north- and south-bound traffic at the San Ysidro border point of entry between San Diego and Tijuana, Mexico after migrants tried to rush the border Sunday.
More than 500 men, women and children overwhelmed Mexican police blockades, prompting U.S. agents to fire tear gas as U.S. Border Patrol helicopters flew overhead.
The Department of Homeland Security Secretary Kirstjen Nielsen said in a statement that the port of entry was closed "to ensure public safety in response to large numbers of migrants seeking to enter the U.S. illegally."
Reuters news agency quoted a Mexican Interior Ministry statement saying it would deport 500 migrants who tried to "violently" and "illegally" breach the border fence. The statement also said Mexico would not deploy military forces to control the migrants.
About 5,000 Central American migrants, many of them attempting to escape poverty and violence in their homelands, have arrived in recent days to Tijuana, just south of the western U.S. state of California, after making their way through Mexico via a caravan.
Earlier, U.S. President Donald Trump implored Mexico and Central American countries Sunday to halt the stream of migrants heading to the United States, even as Mexico denied his claim it was willing to allow U.S. asylum-seekers to stay there until their cases were decided by American immigration courts.
"Would be very SMART," Trump said on Twitter, "if Mexico would stop the Caravans long before they get to our Southern Border, or if originating countries would not let them form (it is a way they get certain people out of their country and dump in U.S. No longer)."
He claimed opposition Democrats "created this problem. No crossings!"
Trump said late Saturday that migrants at the southern U.S. border - most of them from Honduras, Guatemala and El Salvador — "will not be allowed into the United States until their claims are individually approved in court. We only will allow those who come into our Country legally. Other than that our very strong policy is Catch and Detain. No 'Releasing' into the U.S."
He added, "All will stay in Mexico. If for any reason it becomes necessary, we will CLOSE our Southern Border. There is no way that the United States will, after decades of abuse, put up with this costly and dangerous situation anymore!"
But Mexico's incoming government, which assumes power next Saturday, denied that that it is willing to let U.S. asylum-seekers stay there pending the outcome of their cases in U.S. immigration courts.
"There is no agreement of any sort between the incoming Mexican government and the U.S. government,'' future Interior Minister Olga Sanchez said in a statement. She ruled out that Mexico would become a "safe third country" for the migrants trying to reach the U.S.
Hours earlier, however, The Washington Post quoted her as saying that the incoming administration of Andres Manuel Lopez Obrador had agreed to allow migrants to stay in Mexico as a "short-term solution," a plan dubbed "Remain in Mexico."
The White House said, "President Trump has developed a strong relationship with the incoming [Lopez] Obrador Administration, and we look forward to working with them on a wide range of issues."
During the campaign for U.S. congressional elections in early November, Trump decried what he claimed was an "invasion" of immigrants trekking though Mexico toward the United States and dispatched several thousand U.S. troops to the border to block their path.
About 5,000 Central American migrants, many of them attempting to escape poverty and violence in their homelands, have arrived in recent days to Tijuana, just south of the western U.S. state of California, after making their way through Mexico via caravan.
Tijuana Mayor Juan Manuel Gastelum on Friday declared a humanitarian crisis in his border city, which is struggling to accommodate the migrants. Most of the migrants are being housed at a sports complex, where they face long wait times for food and bathrooms.
Trump ordered that immigrants who entered the U.S. illegally, other than through a normal port of entry, would be ineligible for asylum. But a U.S. judge temporarily suspended the order, a decision attacked by Trump.