John Kerry's opposition to the Vietnam War led him to many places, including Paris, where he met with the North Vietnamese in 1970. Kerry said then, and says now, that the meeting was a part of an effort to learn more about U.S. POWs. But some question the propriety of a commissioned Naval officer meeting with the enemy at a time of war.

When Kerry testified before the Senate in 1971, he pushed for an immediate, unilateral withdrawal of U.S. forces. If that happened, he said he knew the North Vietnamese would return all U.S. POWs.

"I have been to Paris. I have talked with both delegations at the peace talks, that is to say the Democratic Republic of Vietnam and the Provisional Revolutionary Government," Kerry said.

Kerry referred to an eight-point withdrawal plan that was offered to the U.S. by Madame Nguyen Thi Binh, then-foreign minister of the Provisional Revolutionary Government. While on his honeymoon in Paris with his first wife Julia Thorne, Kerry met with Madame Binh at a meeting that included members of both delegations to the peace talks, according to Kerry spokesman Michael Meehan.

Explaining Kerry's trip, Meehan said in a statement, "Senator Kerry had no role whatsoever in the Paris peace talks or negotiations. He did not engage in any negotiations and did not attend any session of the talks. Prior to his Senate testimony, he went to Paris on a private trip, where he had one brief meeting with Madame Binh and others. In an effort to find facts, he learned the status of the peace talks from their point of view and about any progress in resolving the conflict, particularly as it related to the fate of the POWs."

Kerry's meeting with Binh occurred while he remained a commissioned officer with the U.S. Navy. Kerry was, by then, a member of the Navy Reserve and not on active duty.

"We've had presidents who have served in the military. We've had presidents who have never served in the military. But we've never had an American president who met with the enemy in a time of war while a naval officer in reserve status. Inconceivable," said John O'Neill, a key member of the anti-Kerry Swift Boat Veterans for Truth (search).

Some critics have suggested Kerry's meeting might have violated the Uniform Code of Military Justice (search), which prohibits members of the armed services from meeting with the enemy at a time of war. Meehan told FOX News the code of military justice did not apply to inactive reserve officers and that Kerry "did nothing wrong." Meehan also said that Kerry met with the North Vietnamese only once.

But historian Gerald Nicosia has written that Kerry met with the North Vietnamese twice.

Citing redacted FBI files, Nicosia said, "The files record that Kerry made a second trip to Paris that summer to learn how the North Vietnamese might release prisoners."

Nicosia told FOX News that the FBI files contained a newspaper clipping about a speech Kerry gave in August 1971saying that he had just returned from a Paris meeting with the North Vietnamese. Nicosia told FOX he discussed the article with Kerry's authorized biographer, Douglas Brinkley, who told him that Kerry had confirmed he'd met with the Vietnamese in 1970 and 1971.

Fox News' Major Garrett contributed to this report.