WASHINGTON (AP) — President Joe Biden and Mexican President Andrés Manuel López Obrador are moving swiftly on new steps to crack down on illegal migration that include tougher enforcement on railways, on buses and in airports as well as increased repatriation flights for migrants from both the U.S. and Mexico.

The two leaders previewed the measures in a statement following a call on Sunday, which centered on their joint efforts to "effectively manage" migration and the U.S.-Mexico border. Biden and López Obrador said they are directing their national security aides to "immediately implement concrete measures" to reduce the number of illegal border crossings.

John Kirby, the White House's national security spokesman, said the U.S. and Mexico will increase enforcement measures that would prevent major modes of transportation from being used to facilitate illegal migration to the border, as well as the number of repatriation flights that would return migrants to their home countries. Kirby also said the U.S. and Mexico would be "responding promptly to disrupt the surges."

Arrests at the U.S.-Mexico border have actually declined in recent months, countering the usual seasonal trends that show migration tends to climb as weather conditions improve. U.S. officials have credited Mexican authorities, who have expanded their own enforcement efforts, for the decrease.

"The teamwork is paying off," Kirby said Tuesday. But he cautioned: "Now we recognize, May, June, July, as things get warmer, historically those numbers have increased. And we're just going to continuously stay at that work with Mexican authorities."

Arrests are up sharply in April on at least one part of the border, San Diego, which appears to have emerged as the busiest corridor for illegal crossings. Arrests in that area totaled 9,513 in the week ended Friday, the third straight increase from 6,695 arrests the first week of April, according to Patricia McGurk-Daniel, the U.S. Border Patrol's San Diego sector chief.

The fresh steps come as Biden deliberates whether to take executive action that would further crack down on the number of migrants arriving at the southern U.S. border.

Since the collapse of border legislation in Congress earlier this year, the White House has not ruled out Biden issuing an executive order on asylum rules to try to reduce the number of migrants at the border. Any unilateral action would likely lean on a president's authority under Section 212(f) of the Immigration and Nationality Act, which offers broad powers to block entry of certain immigrants if their entry is deemed detrimental to the national interest.

Biden administration officials have been poring over various options for months, but the Democratic president has made no decision on how to proceed with any executive actions. White House aides have seen little immediate urgency for the president to take any action, considering the number of illegal border crossings has declined since a record high of 250,000 in December.

The call occurred on Sunday at Biden's request, López Obrador said during his daily news conference Monday in Mexico City.

"We talk periodically," López Obrador said. "I seek him out, he seeks me out, we chat."

The Mexican leader said the two countries have made progress in controlling unauthorized migration by persuading many migrants not to use illegal methods to move from country to country. López Obrador also applauded a January decision by the U.S. Supreme Court that allowed Border Patrol agents to resume cutting razor wire that Texas had installed along the border to try to deter migration.

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Associated Press writers Elliot Spagat in San Diego and Maria Verza in Mexico City contributed to this report.