WASILLA, Alaska (AP) — Alaska Gov. Sarah Palin made a surprise announcement Friday that she is resigning from office at the end of the month without explaining why she plans to step down, raising speculation that she would focus on a run for the White House in the 2012 race.

The former Republican vice presidential candidate hastily called a news conference Friday morning at her home in suburban Wasilla, giving such short notice that only a few reporters actually made it to the announcement. State troopers blocked late-arriving media outside her home, and her spokesman, Dave Murrow, finally emerged to confirm that Palin will step down July 26. He refused to give details about the governor's future plans.

"Once I decided not to run for re-election, I also felt that to embrace the conventional Lame Duck status in this particular climate would just be another dose of politics as usual, something I campaigned against and will always oppose," Palin said in a statement released by her office.

Lt. Gov. Sean Parnell will be inaugurated at the governor's picnic in Fairbanks at the end of the month, Murrow said.

Palin was first elected in 2006 on a populist platform. But her popularity has waned as she waged in partisan politics following her return from the presidential campaign. Her term would have ended in 2010.

Palin said she planned to make a "positive change outside government," without elaborating. She also expressed frustration with her current role as governor.

"I cannot stand here as your governor and allow the millions of dollars and all that time go to waste just so I can hold the title of governor," Palin said.

Later, on Twitter, she promised supporters more details: "We'll soon attach info on decision to not seek re-election ... this is in Alaska's best interest, my family's happy ... it is good. Stay tuned"

Palin's decision even took Parnell by surprise. He said he was told on Wednesday evening, and was not aware that any presidential ambitions were behind the move.

Palin emerged from relative obscurity nearly a year ago when she was tapped as then Republican presidential candidate John McCain's running mate.

She was a controversial figure from the start, with comedian Tina Fey famously imitating her elaborate hairstyle and folksy "You betcha!" on "Saturday Night Live."

Most recently, she led a public spat with "Late Show" host David Letterman over a joke he made about one of her daughters being "knocked up" by New York Yankees baseball player Alex Rodriguez during the governor's recent visit to New York. Palin's 18-year-old daughter, Bristol, is an unwed, teenage mother.

Letterman later apologized for the joke.

Palin's family and the ridicule they endure being in the public eye was part of her decision. She complained that her 14-month-old son, Trig, who was diagnosed with Down's syndrome, had been "mocked and ridiculed by some mean-spirited adults recently." She didn't elaborate.

Palin campaigned on ethics reform in the 2006 election, defeating incumbent Gov. Frank Murkowski in the Republican primary and a former two-term Democratic governor, Tony Knowles, in the general election.