U.S. Customs and Border Protection officials announced Friday that they would begin sending flights of between 120 and 135 migrants to San Diego from the Rio Grande Valley, saying Border Patrol stations there are overwhelmed by a surge in migrant apprehensions.

The flights began last week, and the agency said it is planning three such flights per week going forward.

San Diego County Supervisor Dianne Jacob said in an email she was "deeply concerned" that the additional migrants flown to San Diego would put an even greater strain on local nonprofits and taxpayers.

"Immigration is clearly the responsibility of the federal government, but now it's sticking San Diego County with the bill," Jacob said. "Since the opening of an emergency shelter downtown in October, the county has had to spend nearly $2 million to screen and process some 14,000 asylum seekers. Local taxpayers should not be on the hook for this."