Alaska Lt. Gov. Byron Mallott resigned Tuesday over unspecified inappropriate comments, complicating what was already a difficult re-election fight for Gov. Bill Walker.

Mallott, in his resignation letter, said his decision was "compelled by inappropriate comments I made that placed a person whom I respect and revere in a position of vulnerability."

He apologized and acknowledged that his actions had compromised Walker's ability to lead the state.

The nature of the comments remained unclear.

Mallott did not immediately return a phone message seeking details, and Walker did not take questions during a news conference with Mallott's successor, Valerie Davidson. Until Tuesday, she had served as the state health commissioner.

Walker's office also provided few details. In a statement, Walker said he learned late Monday that Mallott -- a man with whom he has shared a brother-like bond -- had made comments not suitable for his office.

"As leaders, we must hold ourselves to the highest standards of conduct," Walker said.

The resignation was announced shortly after Walker participated in an at-times testy debate in Anchorage with his two chief rivals, Democrat Mark Begich and Republican Mike Dunleavy.

Davidson said she was "deeply saddened" by Mallott's resignation and "profoundly disappointed by his conduct."

"Respect for women, and the dignity of all Alaskans, is our responsibility," she said in a release.

Walker, in a separate statement, said it's too late for Mallott to remove his name from the ballot but that Mallott would not accept the position of lieutenant governor if elected. He said Davidson would assume the role of his running mate.

Walker campaign manager John-Henry Heckendorn said the campaign has been in conversations with Begich's campaign for several days about a "path forward for Alaska." He declined to go into details, but he said the conversations were prompted by concerns about Dunleavy and the dynamics of a three-way race. The talks so far have been "inconclusive" but will continue, Heckendorn said.

Libertarian Billy Toien also is running. A message was left with Begich's campaign manager.

Mallott and Walker had forged a tight bond since joining forces as part of a unity ticket in 2014. That year, they each were running for governor and saw joining together as their best shot at defeating Republican Gov. Sean Parnell.

As part of the arrangement, supported by state Democrats, Walker changed his party affiliation from Republican to undeclared and Mallott, a Democrat, abandoned his gubernatorial ambitions to be Walker's running mate. They narrowly won.

On Tuesday, as Walker and Davidson held their brief news conference at the governor's office in Anchorage, the largest gathering of Alaska Natives in the state was being held nearby at the city's convention center.

Word of Mallott's resignation was beginning to circulate among the delegates at the Alaska Federation of Natives conference, where Mallott, an Alaska Native leader from southeast Alaska, had long been treated as a rock star.

"Oh my God!" said Victoria Campbell when informed of Mallott's use of inappropriate comments. Then she asked what was on the minds of many Alaskans: "Towards who?"

The Democrat from Gambell, located on St. Lawrence Island in the Bering Sea between Russia and the United States, said she didn't know enough to comment on the resignation but did say it wouldn't affect her vote for Walker.