WASILLA, Alaska — 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"