The Border Patrol said Tuesday that its agents have been assaulted 250 times along the Mexican border since Oct. 1, up 38 percent from 181 attacks during the same period last year.
The agency's San Diego sector, which encompasses western California, reported the steepest increase.
Assaults more than quadrupled to 110 from Oct. 1 through Sunday, up from 24 the same period last year.
Agents are attacked with rocks, vehicles and "Molotov cocktails" of bottles filled with flammable liquid that explode when they hit the ground, the agency said.
The Border Patrol said agents are increasingly being attacked from people in Mexico, where they have "little to no fear of apprehension or arrest by Mexican authorities."
The agency recently equipped agents in California and Arizona with a powerful, pepper-spray launcher that has a range of more than 200 feet.
It has also fired tear gas into Tijuana, Mexico, several times in response to attacks.
"Criminals are discovering they can no longer operate with impunity in certain areas and are systematically being prevented from using the border for their criminal activities," Border Patrol Chief David Aguilar said in a press release.
The Border Patrol said agents were attacked 987 times during the 12-month period that ended Sept. 30, the highest since it began keeping track in the late 1990s.
U.S. officials say the rising violence indicates smugglers are frustrated and more desperate as it has become more difficult to cross the border illegally.