FITCHBURG, Wis. — Gov. Scott Walker said Tuesday that he's established a "clear distinction" in his office between state business and illegal campaign work on the taxpayer dime.

Blurred lines between political work and official government operations by Walker's top aides led to a three-year investigation into the Milwaukee County executive office under Walker that ended a year ago. Walker's deputy chief of staff was convicted of misconduct in office for doing campaign work on the taxpayer dime and five Walker aides and associates were convicted on other charges.

Walker said ever since he took office as governor in 2011 he carries two cellphones — one for personal use and one for official state business — and requires all of his cabinet secretaries and staff to go through ethics training and sign a document saying they understand they can't campaign on state time.

"We have a clear distinction between things that are political and official," Walker said Tuesday following an event marking the opening of a new grocery store.

Walker wasn't charged in the probe into his county executive office that ended last year. But the release last week of 28,000 pages of documents collected during the investigation are leading to a new round of questions about illegal campaign work going on in Walker's county executive office.

Walker's comments Tuesday were his first in Wisconsin since the release of the documents.

The code of conduct agreement that Walker requires his cabinet secretaries and staff to sign prohibits them from performing campaign activities between the hours of 8 a.m. and 5 p.m.

"If an urgent issue comes up that you cannot address during off-hours, you must obtain pre-approval before engaging in that activity," the document says. "You should never use state resources to do campaign work, including a work blackberry, work computer, work phone, or work e-mail."

It lists 14 specific campaign activities that are not permitted, including fundraising, preparing campaign advertising and working with campaign volunteers. Failure to adhere to the terms can result in termination, the form says.

Walker's spokesman Tom Evenson said there have been no campaign-related violations, but Department of Transportation assistant deputy secretary Steven Krieser was fired for a violation of the professionalism/personal conduct provision.

Walker fired Krieser in August after he made Facebook posts calling immigrants in the U.S. without legal permission criminals and likening them to Satan.

Krieser had signed the document in November 2011, which is when Walker first required staff and top cabinet officials to sign it, Evenson said.

The Associated Press also asked for a list of all signed copies of the document but that information was not immediately available.

Walker said that since becoming governor, he has carried two cellphones to separate official and personal business.

When asked why he didn't do that when he was county executive and running for governor, Walker said: "Because I just had one phone so I kept it all together."

Walker has repeatedly said he didn't know that his county staff had erected a secret wireless network in his office to evade the state open records law. But evidence collected during the investigation, including emails released last week, show that Walker sent and received emails from county workers during normal business hours in which campaign issues were discussed. The lead investigator also testified that Walker must have known what was going on.

Walker has denied knowing there was illegal activity happening in his office. As to whether he should have known, or was also engaged in illegal campaign work, Walker points to the fact that he wasn't charged in the investigation led by Milwaukee County District Attorney John Chisholm, a Democrat.

"Don't look at anything I say, look at what a district attorney's office did," Walker said. "Not one that was of my own party, but one that's led by a Democrat."

Democrat Mary Burke, who is running against Walker this year, said on Monday that he had set a "low bar for campaign ethics."

"As governor I'm going to make sure that I bring back the trust and honesty that we deserve for the highest office," Burke said in Green Bay.

When asked Tuesday, Walker declined to respond to her comments.

Last week the Republican Governors Association launched a statewide ad attacking Burke. The RGA has spent $1.2 million on the buy so far, according to a tally by the liberal group One Wisconsin Now.