WASHINGTON – The Obama administration’s top environmental official in the oil-rich South and Southwest region has resigned after Republicans targeted him over remarks made two years ago when he used the word “crucify” to describe how he would go after companies violating environmental laws.

In a letter to Environmental Protection Agency Administrator Lisa Jackson sent Sunday, Al Armendariz says he regrets his words and stresses that they do not reflect his work as administrator of the five-state region including Texas, New Mexico, Oklahoma, Arkansas and Louisiana. Armendariz, who holds a doctorate in environmental engineering, apologized last week for his remarks.

A senior administration official, speaking on condition of anonymity because of the sensitivity of the subject, told The Associated Press that Armendariz has since received death threats.

His resignation was effective Monday, when he informed his senior staff.

“I have come to the conclusion that my continued service will distract you and the agency from its important work,” Armendariz wrote in the letter, which was obtained by the AP.

Republicans in Congress had called for Armendariz’ firing, after Oklahoma Sen. James Inhofe highlighted the May 2010 speech last week as proof of what he refers to as EPA’s assault on energy, particularly the technique of hydraulic fracturing, or fracking.

At a town hall meeting in Washington on Friday, Jackson had said only that she would continue to review the case, calling Armendariz’ words “inflammatory” and “wrong.”

President Obama appointed Armendariz in November 2009, at the urging of Texas-based environmental groups. He is one of the few Latinos in senior leadership at the EPA.

The EPA, perhaps more than any other agency, has found itself in the GOP’s crosshairs over its regulation of the gases blamed for global warming, steps it has taken to limit air pollution from coal-fired power plants, and its increased regulation of fracking, which is responsible for a gas drilling boom.

Republicans, including presidential contender Mitt Romney — who has called for Jackson herself to be fired — have blamed the agency for high gasoline prices and clamping down on American energy.

Environmentalists said Monday that it was Armendariz getting crucified for doing his job — enforcing the law.