Madison -- Gov. Scott Walker will not challenge any signatures by Monday's deadline in an attempt to stop a recall election against him.

That leaves only a review by state elections officials standing between the Republican governor and only the third recall election for a governor is U.S. history. An independent conservative group released its own analysis of the recall petitions Monday, but state elections officials said the law does not allow it to count those outside challenges.

"We are not filing any specific challenges to any specific signatures today," Walker campaign spokeswoman Ciara Matthews said. "We simply ran out of time."

Organizers gathered more than 1 million signatures in 60 days seeking to force the recall – well over the 540,000 valid signatures needed. Over the last month, Walker and Republicans have been examining the signatures seeking to find ones to challenge as invalid.

In a filing Monday, Walker's campaign called on the elections agency to continue its official review of the signatures.

Government Accountability Board spokesman Reid Magney confirmed that the elections agency would continue that review, including the search for incomplete, duplicate or fraudulent signatures. Currently, the agency has until March 19 to complete that review but Magney said he wasn’t sure how much time it would take.

“That’s something we’re obviously still working on,” Magney said.

Scot Ross, a spokesman for former Dane County Executive Kathleen Falk, a Democrats seeking to challenge Walker, called for the accountability board to complete its review by March 19. He said Walker's decision not to file challenges shows enough signatures were gather.

"It shows he knows the recall election is coming and it's coming soon," Ross said.

If the board concludes that the signatures are valid, the election would be ordered for essentially six weeks later. If there is a primary election, it would be held on that date with the general election four weeks after that.

Walker had 10 days under state law to challenge signatures and a Dane County judge granted him an additional 20 days. But Walker was turned down when he sought two more weeks to examine the roughly 150,000 pages of signatures.

"That put us in an impossible timeline," Matthews said.

Mike Tate, chairman of the Democratic Party of Wisconsin, said Monday that Walker had been given three times as much time as normally allowed under state law. He said the governor's decision not to challenge the signatures discredits previous claims by Republicans that there was widespread fraud in the petition process.

The state Republican Party has released a few examples of fraud in the recall petitions, such as the appearance of the name Donald Duck. State GOP spokesman Ben Sparks said Monday he wasn't sure if Republicans would release the full results of the petition review the party did with Walker's campaign.

Walker's filing with the accountability board said that GOP volunteers have reviewed about 350,000 of the signatures and found problems with 10% to 20% of them that need further checking. That's consistent with the Journal Sentinel's own analysis of a sample of the petitions.

The newspaper’s analysis used a random sample of 500 signatures and found problems with about 15% of those. The newspaper's review was more rigorous than the verification process being conducted by the accountability board.

"We've said all along that we anticipated there would be enough signatures to force a recall election," Matthews said.

Separately Monday, the groups True the Vote and Verify the Recall released their own analysis of the recall signatures against Walker. The governor asked in his filing with the accountability board that state officials take that analysis into account.

But Magney said that the accountability board is not allowed by state law to do so.

"There is no legal basis for us to accept third-party challenges," Magney said.

Mark Graul, a GOP strategist who ran Mark Green's unsuccessful race for governor in 2006, said that Republicans know a recall will happen and are preparing for it.

Graul said he didn't believe that Walker or his opponents would benefit greatly by seeking to hold a recall election quickly or by seeking to draw out the process.

"I'm not sure there's a strong strategic advantage either way," Graul said.