LINCOLN, Neb. (AP) -- Nebraska Lt. Gov. Rick Sheehy resigned Saturday after "breaking the public trust," Gov. Dave Heineman said.

Heineman announced Sheehy's resignation in a hastily called news conference Saturday morning. Heineman said the resignation followed disclosures made in a public records request, but declined to discuss what those disclosures were.

"As public officials, we are rightly held to a higher standard," Heineman said. "I had trusted him, and that trust was broken."

The Omaha World-Herald reported (http://bit.ly/X2LVyC) that Sheehy resigned after it raised questions about improper cellphone calls to four women, none of which were his wife, during the past four years. The World-Herald said in its online additions Saturday that it discovered Sheehy made thousands of late-night calls to the women on his state-issued cellphone.

Sheehy, a Republican, had been considered the front-runner in the 2014 gubernatorial race and had been endorsed by Heineman. Sheehy has been traveling throughout the state, making speeches and holding public events.

Sheehy was the mayor of Hastings before Heineman selected him as his running mate. They were elected by a record margin to their first full term in 2006 and re-elected in 2010.

Last July, Sheehy's wife, Connie Sheehy, filed for divorce after nearly 29 years of marriage. Her divorce filing stated the "marriage of the parties is irretrievably broken."

Asked for his reaction Saturday, Heineman said "I've got a knot in my stomach. I'm deeply disappointed."

Heineman said he doubted Sheehy would run for the governor's office now.

"And no, I would not support him under the circumstances," Heineman said.

Sheehy did not appear at the news conference, and Heineman declined to answer questions about what had occurred that led Sheehy to resign.

"You'll have to ask him about that," Heineman told reporters. A phone call to Sheehy's office went unanswered, and a message was not immediately returned.