Border Patrol apprehended more than 200,000 migrants crossing the US-Mexico border unlawfully in September, according to a Homeland Security official, marking the highest total this year and underscoring the ongoing challenges for the Biden administration amid mass migration in the region.

Federal authorities are grappling with a new surge of migrants which has strained federal resources and fueled concerns in cities nationwide. Last month's border arrests mark an increase from August, when Border Patrol arrested around 181,000 migrants crossing between ports of entry. It's the highest total since December, when Border Patrol apprehended more than 222,000 migrants.

Migrant crossings at the US-Mexico border are expected to remain high in the near term, a senior US Customs and Border Protection official recently told CNN, noting that additional commitments from Mexico are expected to help eventually drive down numbers.

A Department of Homeland Security spokesperson said in a statement, "We remain vigilant and expect to see fluctuations, knowing that smugglers continue to use misinformation to prey on vulnerable individuals."

"We are safely and efficiently vetting and processing migrants to place them in immigration enforcement proceedings consistent with our laws and operational planning efforts," the spokesperson added. "DHS has used its executive authorities to improve processing, strengthen consequences at the border, and more quickly remove individuals who fail to establish a lawful basis to remain in the country."

The Department of Homeland Security has repatriated over 281,000 individuals since May while "expanding refugee processing and family reunification options," the spokesperson said.

This week, Secretary of State Antony Blinken, along with Secretary of Homeland Security Alejandro Mayorkas, Attorney General Merrick Garland and White House Homeland Security adviser Dr. Liz Sherwood-Randall will meet with their Mexican counterparts in Mexico City for annual security talks.

Migration is expected to be a topic of discussion. Senior administration officials maintain that the US has been in regular touch with Mexico over the situation at the US southern border, including commitments to shore up enforcement.

This story has been updated with additional details.