In a private conversation made public by a live microphone, President Obama appeared to be putting off diplomatic talks with Russian leaders about a controversial missile defense system in Eastern Europe until after the November election, prompting quick attacks from the president's Republican rivals.

Obama was seen on video Monday in a casual chat with Russian President Dmitry Medvedev at a nuclear security summit in Seoul. On the tape, Obama leans toward Medvedev and can be heard giving him a message for the once and future Russian president, Vladimir Putin.

"On all these issues, but particularly missile defense, this can be solved," Obama said. "But it's important for him to give me space.

"This is my last election. After my election I have more flexibility."

"I understand," Medvedev responded. "I will transmit this information to Vladimir."

The exchange, its air of secrecy enhanced by the muffled audio, raised alarm among Obama's critics about his long-term commitment to the missile defense system. The U.S. has promoted it as a shield to protect Europe from missile attacks by Iran. The Russians fear it's aimed at them, and opposition to the missile shield was a major theme of Putin's recent presidential campaign.

Putin, who previously served two four-year terms as president, won a new six-year term March 5 in an election that critics charge was flawed. He will succeed Medvedev, who replaced him in 2008 when term limits prevented Putin from seeking a third successive term.

Mitt Romney, the front-runner for the Republican nomination, accused Obama of "pulling his punches with the American people" and obscuring his plans for the missile defense system.

GOP presidential candidate and former House Speaker Newt Gingrich said it suggests that Obama is prepared to "sell out" America.

House Speaker John Boehner, R-Ohio, said "we look forward" to hearing what the president meant by "more flexibility" when he returns from South Korea.

By afternoon, the Republican National Committee had created a video ad with the subtitle, "What Obama tells world leaders when he thinks you aren't listening."

White House aides said the president was still "deeply invested" in the missile defense system.

Deputy National Security Adviser Ben Rhodes said after the recording became public that the two leaders had been talking about Russia's objections to the missile defense system and agreed to talk later because of political concerns on both sides. The two sides have been trying in vain for years to reach a breakthrough on missile defense, and no one was expecting a dramatic change at this week's nuclear summit.

What Obama meant by "flexibility" was unclear. Some analysts speculate the U.S. might try to win over the Russians by showing them classified data to prove that the system could take down convince the Russians.

Public broadcast of the private exchange provided a rare glimpse at the candor world leaders sometimes exhibit at such high-level meetings. Last year, journalists overheard Obama and French President Nicolas Sarkozy talking about Israeli Prime Minister Benjamin Netanyahu. Sarkozy said he "can't stand" Netanyahu.