Obama, the Democrat, said Kissinger favored talking with Iran without preconditions. McCain, the Republican, challenged the assertion.

Kissinger -- who is an adviser to McCain -- said at a CNN seminar in Washington this month that he favored high-level talks, likely at the secretary of state level, but was less specific about the pre-conditions that McCain and Obama were at odds over Friday night.

Kissinger's quote, CNN said, was that the United States needed to engage Tehran at a high level.

"One utility of negotiation is to put before Iran our vision of a Middle East, of a stable Middle East, and our notion on nuclear proliferation at a high enough level so that they have to study it," Kissinger said. "And, therefore, I actually have preferred doing it at the secretary of state level."