A U.S. senator insists he is not gay despite having pleaded guilty to a disorderly conduct charge stemming from a June incident in a Minneapolis airport men's room with an undercover police officer.

"I did nothing wrong in the Minneapolis airport," Larry Craig, R-Idaho, told a news conference in Boise, Idaho on Tuesday.

"I did nothing and I regret the decision to plead guilty and the sadness that decision has brought on my wife, my family, friends, staff and fellow Idahoans. And for that, I apologize."

Roll Call, a newspaper covering Capitol Hill in Washington, reported the arrest on Monday.

The Associated Press obtained the prosecutor's complaint.

According to the document, airport police Sgt. Dave Karsnia had been investigating allegations of sexual activity in airport washrooms.

On June 11, he was sitting in one stall, and saw Craig staring at him through the crack in the door.

When another man left, Craig entered the stall adjacent to Karsnia and tried to obscure the front with his roller bag.

Craig then tapped his right foot several times, eventually putting it in the officer's stall and touching Karsnia's foot. According to the complaint, Karsnia recognized that "as a signal often used by persons communicating a desire to engage in sexual conduct."

When Craig passed a hand under the stall divider and slid it to the front three times, Karsnia then showed Craig his police ID under the divider, prompting an exclamation of "No!," the document said.

On Aug. 8, Craig pleaded guilty to a charge of disorderly conduct. The Hennepin County, Minn. court dismissed a charge of gross misdemeanour interference to privacy.

The court imposed fines and fees of US$575 on Craig and put him on unsupervised probation for a year. A 10-day sentence in the county workhouse was stayed.

"In June, I overreacted and made a poor decision," Craig said Tuesday. "While I was not involved in any inappropriate conduct at the Minneapolis airport or anywhere else, I chose to plead guilty to a lesser charge in order to make it go away."

Craig said he sought no counsel -- a mistake he regrets. He has now hired a lawyer to advise him how to proceed.

In the eight months prior to June 11, "my family and I have been viciously harassed by the Idaho Statesman," he said.

For its part, the paper published an editorial on Tuesday calling for Craig to explain himself to Idahoans.

"On the surface, it seems implausible that any educated professional -- much less an elected official -- would face criminal proceedings without hiring an attorney," it said.

According to the police report, Craig showed Karsnia his Senate business card and asked him, "What do you think about that?" The newspaper said if true, "this suggests an inexcusable abuse of power."

Allegations of homosexual behaviour have dogged Craig, a rancher and member of the National Rifle Association, since the 1980s.

In a May interview with the Idaho Statesman, Craig -- who has voted against gay marriage -- denied such allegations published on a gay activist's blog.

"I am not gay. I have never been gay," Craig said Tuesday. "Still, without a shred of proof or evidence to the contrary, the Statesman has engaged in this witch-hunt."

Some other GOP senators are facing related problems.

Sen. Ted Stevens, R-Alaska, is under fire for his relationship with a contractor who more than doubled the size of Stevens' home.

Sen. David Vitter, R-La., has acknowledged that his phone number appeared in the records of a Washington-area business that reportedly was a prostitution front.

In 2006, a furor erupted when it became known that Mark Foley, then a Florida Republican congressman, had been sending sexually explicit messages to male congressional pages. In addition, some in the Republican congressional leadership knew about it and did nothing.

Citizens for Responsibility and Ethics in Washington, a watchdog group, filed a complaint Tuesday with the Senate ethics committee over Craig's behaviour. The group wants an investigation into whether Craig violated Senate rules by engaging in disorderly conduct.

Craig was expected to announce this fall whether he will seek a fourth Senate term in 2008. He confirmed he will issue a statement later this fall.

The senator had been a prominent supporter of Mitt Romney, a leading Republican presidential hopeful, but has ended his role as the candidate's liaison in the Senate.

"He did not want to be a distraction and we accept his decision," said Matt Rhoades, a Romney campaign spokesman.

With files from The Associated Press