U.S.. Rep. Kevin Yoder of Kansas on Monday apologized again, and repeatedly, for skinny-dipping in the Sea of Galilee during a congressional fact-finding trip to Israel last year.

"I made the real mistake of going in without clothing," Yoder said during an interview on KCUR's "Up to Date."

"It's a regrettable incident. ... Some folks may be very disappointed in my behavior."

Meanwhile, the Chicago Tribune reported that the FBI says its agents are not investigating any criminal wrongdoing related to the Israel trip. Earlier, in revealing the incident, the website Politico reported that the agency had investigated the trip.

And in a joint interview in New Hampshire on Monday, presumptive Republican presidential nominee Mitt Romney and running mate Paul Ryan denounced the swimming.

"It's reprehensible," Romney said. "It's another terrible mistake by individuals."

"This is unbecoming of a member of Congress," Ryan said. "It's behavior that shouldn't be tolerated. I think they know that."

Kansas Democratic Party Chairwoman Joan Wagnon said the congressman should resign immediately "and not subject Kansas to any further embarrassment." Yoder is a Republican.

Yoder was one of about 20 members of a congressional traveling party who reportedly jumped into the lake following dinner at a seaside restaurant attended by House Majority Leader Eric Cantor and other GOP leaders. Cantor did not participate in the post-dinner dip.

Yoder, 36, was reported to be the only member of the party who swam naked. Yoder said he was in the water about 10 seconds. He also said that although he and his wife, Brooke, drank wine during dinner, he was not drunk when the incident occurred.

"Alcohol really played no role in the decision to go in," Yoder said. "It was really much more of a spontaneous moment."

He added, "I've never done that before, and I can tell you I'll never do that again."