Republican Sen. John Ensign is apologizing for the pain his extramarital affair has caused but is withholding detailed comment on the issue.
In a statement issued late Friday, Ensign said potential investigations into his actions concerning the affair with former campaign aide Cindy Hampton make public comment inadvisable.
Citizens for Responsibility and Ethics in Washington, a government watchdog group, has called for investigations into Ensign.
"I know there are questions regarding my affair with Cindy Hampton that people want to know the answers to," Ensign said. "It was reported, however, that CREW was planning to file complaints with the Senate Ethics Committee and the Federal Election Commission, so I have been advised not to publicly comment further at this time."
CREW alleged last month that Ensign violated the Senate's ethics rules by engaging in an affair with Hampton, who was an aide and married to his administrative assistant, Doug Hampton, then terminating their employment.
The group also said Ensign violated ethics and campaign finance rules by failing to report a severance payment to the woman as an in-kind contribution from his campaign or leadership political action committee.
It has filed complaints with the Senate Ethics Committee and the FEC, asking them to investigate.
"If any inquiries are undertaken, then I am confident they will be resolved in my favor and those questions will be answered," Ensign said.
"I am very sorry this issue has caused a great deal of embarrassment and pain for my family, the Hamptons, and many of my supporters. I remain committed to working hard for the people of Nevada on the important matters before the Senate."
Ensign resigned is position as head of the Republican Policy Committee one day after acknowledging the affair between December 2007 and August 2008 with Hampton. The head of the committee is No. 4 in the GOP's leadership hierarchy.
According to Ensign's lawyer, the senator's parents gave the Hampton family $96,000 in April 2008 as a gesture of generosity after they learned about the affair.
CREW has said that payment also should be investigated by authorities.