A Republican congressional candidate whose campaign is being investigated for sending intimidating letters to Hispanic voters lashed out at his Democratic rival, saying she was fueling the uproar over the mailings.

Tan Nguyen on Sunday rejected calls to drop out of the race to unseat longtime Rep. Loretta Sanchez, and implied the popular congresswoman was behind the probes into the letters warning immigrants they could be deported or jailed for voting in next month's election.

"There has been no crime committed so why is there a criminal investigation three weeks prior to a very important election?" Nguyen asked. "What is going on? Who is fueling this investigation?"

Nguyen, a Vietnamese immigrant who has made illegal immigration a centerpiece of his campaign, said he would stay in the race despite calls from the state GOP and others to quit.

"I'm innocent," Nguyen said. "I'm not going to quit this race; I'm going to win this race."

Nguyen said Sunday he did not authorize or approve the letters, which warn in Spanish: "You are advised that if your residence in this country is illegal or you are an immigrant, voting in a federal election is a crime that could result in jail time."

In reality, immigrants who have become naturalized U.S. citizens are eligible to vote.

California Department of Justice investigators searched Nguyen's campaign headquarters on Friday, as well as his residence and a home listed as belonging to one of his staffers. Investigators are looking into possible voting rights violations.

Nguyen also said he regretted firing his office manager who sent the mailings and publicly invited her to return.

Nguyen said Sanchez was "fueling this hysteria" and investigators were "terrorizing my family and volunteers" and violating his right to free speech. A voicemail message left at Sanchez's office was not immediately returned.

William Braniff, a spokesman for the Nguyen campaign and a former U.S. Attorney, blamed the controversy on the media, whom he said had mistranslated the word "emigrado," which appeared in the Spanish-language letter.

The word "emigrado" refers to someone who has emigrated and has no specific legal connotation.

Braniff said, however, the word refers specifically to legal residents -- but not naturalized citizens. He said when the letter was translated into English, the word "emigrado" became "immigrant" and didn't distinguish between those immigrants who were U.S. citizens and U.S. residents.

Braniff did acknowledge that the letter originated in Nguyen's office. He declined to give further details, citing the ongoing state and federal probes.