Mexico and the United States broke up a counterfeiting ring that printed an estimated $5 million in fake $100 bills in Mexico and sold them across the border, officials said Wednesday.

The ring, based in the western state of Jalisco, operated more than four years, selling fake $100 bills in Santa Ana, Calif., San Diego, Calif, and Phoenix, Ariz., said Jose Luis Marmolejo, of the attorney general's organized crime division.

The bills, produced with offset printing equipment, were "one of the best falsifications we've seen," Marmolejo said.

Authorities arrested six people, including a man they believe is a former state police officer, and seized nearly $400,000 in fake bills in raids last Friday in Jalisco state, he said.

Last Friday, U.S. Secret Service agents arrested 10 people and seized $75,000 during raids on three houses in Santa Ana, Calif., according to U.S. Assistant U.S. Attorney Robert Keenan. Keenan said 13 people were indicted in the United States on charges of selling the counterfeit bills.

The arrests capped a joint two-year investigation, Marmolejo said.

Mexican authorities also seized six guns of different calibers, ammunition, printing equipment and printing chemicals during the raid on eight buildings in Jalisco, he said.