SAN FRANCISCO, Feb. 1 (Xinhua) -- U.S. federal immigration authorities have launched a massive raid in 77 businesses for illegal jobs in North California this week, they said Thursday.

Immigration and Customs Enforcement (ICE) agents said in a statement it launched the raid on Jan. 29-31 in 77 workplaces in the areas of San Jose, San Francisco and Sacramento on the U.S. west coast amid reports of its massive sweep in the region for undocumented immigrants.

Special agents of Homeland Security Investigations (HSI), a division of the ICE, served notices of inspection, the ICE said.

"The actions taken this week reflect HSI's stepped-up efforts to enforce the laws that prohibit businesses from hiring illegal workers," it said.

The ICE raid came less than a month after ICE agents swept into nearly 100 7-Eleven convenience stores nationwide and arrested 21 suspected undocumented immigrants.

Since then rumors have been rampant that the federal immigration authorities will start a massive sweep in North California, a move seen as targeting undocumented immigrants in sanctuary cities where they are protected under a local "sanctuary policy."

U.S. President Donald Trump has vowed to deport those undocumented immigrants in sanctuary states or cities since he took office last year.

Trump's policy has strained relations between federal government and the sanctuary states and cities, which defiantly offered protection to those undocumented immigrants.

The ICE did not specify whether its actions were part of the previously planned massive sweep, but its moves to audit so many businesses in the last three days in a single area of responsibility were still regarded as unprecedented.

San Francisco District Attorney George Gascon told local TV KRON4 that the ICE's actions have frightened many undocumented immigrants.

"We had victims clearly telling us I'm not cooperating with those guys because I'm not going to go to court and be subjected to potentially being arrested," he said, referring to victims of domestic violence who were reluctant to report their sufferings to police for fear of possible deportation from the United States.

ICE Spokesman James Schwab said the agency's raids "remain ongoing" and "Any potential criminal charges or other penalties will be coordinated with the U.S. Department of Justice."

ICE inspections can lead to fines for businesses and criminal arrests of employers, in addition to immigration arrests of undocumented workers.