FILE - In this Jan. 9, 2014 file photo, New Jersey Gov. Chris Christie, second left, arrives at Fort Lee, N.J., City Hall. Christie traveled to Fort Lee to apologize in person to Mayor Mark Sokolich. Many people have known little about Fort Lee until a political scandal centering on Christie enveloped the borough. Now for residents of the New York City bedroom community defined by both a feisty pride and frustration over the mixed blessings of proximity to the George Washington Bridge, the scandal is the reminder they did not need of how the bridge dictates the rhythm of everyday life. (AP Photo/Richard Drew, File)

TRENTON, N.J. - New Jersey's Republican Gov. Chris Christie fired one of his top aides and apologized for his staff's "stupid" behaviour, in an attempt to limit damage over charges his administration engineered traffic jams in a political vendetta that could now undermine his presidential prospects.

The escalating controversy could damage the governor's national reputation and give opponents an opportunity to portray him as a ruthless bully.

"I am who I am. But I am not a bully," Christie declared during a lengthy news conference Thursday.

Christie, who had previously said his staff had nothing to do with the lane closings in September that caused major backups at the George Washington Bridge, which links New York and New Jersey, said he fired Deputy Chief of Staff Bridget Anne Kelly "because she lied to me" when he demanded weeks ago that anyone who knew anything about the episode come forward.

"I am embarrassed and humiliated by the conduct of some of the people on my team," he said as he addressed the widening scandal that could cast a shadow over his expected run for the White House in 2016.

The famously blunt Republican fielded dozens of questions from reporters with uncharacteristic patience during a nearly two hour press conference.

Kelly was the latest casualty in the scandal. Two other top Christie appointees have resigned in the past few weeks.

The investigation broke wide open on Wednesday, with the release of emails and text messages that suggested Kelly arranged the traffic jams to punish Fort Lee's mayor for not endorsing Christie for re-election.

The political-payback allegations turned a local traffic furor into a national issue and raised questions about Christie's leadership and integrity as he lays the groundwork for a White House bid. Democrats at the national level have seized on the scandal as more evidence that Christie is a bully.

The governor brushed off questions about the effect on his presidential prospects, saying he was too busy governing the state to think about that.

Afterward, some political analysts on both sides of the aisle said Christie would probably pull through OK — provided there are no more surprises.

Democratic operative David Axelrod complimented Christie for handling the news conference "as well as he could," writing on Twitter: "Unless smoking gun turns up tying him to scheme, or others arise, he lives 2 fight another day."

Christie said he is still looking into the traffic-jam episode and will take action against other senior staff members if it is warranted.

The chief federal prosecutor in New Jersey, U.S. Attorney Paul Fishman, said he is "reviewing the matter to determine whether a federal law was implicated." The Legislature is also investigating. Using public resources for political ends can be a crime.

Christie said he saw the emails and text messages for the first time on Wednesday, and was "blindsided" by what he read and outraged by the callous language. He said he was left "heartbroken" and "betrayed" by his tight-knit circle of advisers.

"I had no knowledge or involvement in this issue, in its planning or execution," Christie said of the lane closings. "And I am stunned by the abject stupidity that was shown here."

Kelly hasn't commented. Christie said he hadn't spoken to her or asked to hear her side of the story since the emails were released, saying he didn't want to be accused of trying to influence a possible witness.

"Time for some traffic problems in Fort Lee," Kelly wrote in August in a message to David Wildstein, an official with the Port Authority of New York and New Jersey.

"Got it," Wildstein replied. A few weeks later, Wildstein closed two of three lanes connecting Fort Lee to the George Washington Bridge, which runs between New Jersey and New York City and is one of the busiest spans in the world, crossed by more than 100 million vehicles a year.

In the back-and-forth emails and text messages that followed, Christie loyalists gloated over the traffic jams and called the Fort Lee mayor "an idiot" and "this little Serbian."

Wildstein, a Christie appointee who resigned from the Port Authority of New York and New Jersey after being implicated in the scandal, was found in contempt Thursday by a legislative committee after he invoked his right against self-incrimination and refused to answer questions. The Port Authority operates the bridge.

Christie travelled to Fort Lee later in the day and apologized in person to Mayor Mark Sokolich.

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Associated Press writer Steve Peoples in Washington contributed to this report.

News from © The Associated Press, 2014