U.S. President Barack Obama on Monday, March 26 told President Dmitry Medvedev that he had little flexibility to address Russia's objections to a U.S. missile defence shield before his November reelection bid, AFP said.

Obama was picked up on an open mic privately explaining his position to Medvedev in an exchange heard by some reporters, during their meeting on the sidelines of the nuclear security summit in Seoul.

The U.S. leader told Medvedev, in their last meeting before Vladimir Putin is inaugurated president in May, that on all issues, but particularly missile defense it was important for Russia to give him "space."

Medvedev replied "Yeah, I understand. I understand your message about space," according to a transcript of the exchange carried by ABC News.

"This is my last election. After my election I have more flexibility," Obama said, pledging to "transmit this information to Vladimir."

The exchange appeared to indicate that Obama believes he has little leverage to conclude deeply divisive foreign policy election issues in a campaign year, and also that he is confident he will win reelection.

The White House insisted it was committed to implementing the missile defense shield, despite Russian objections but said the longstanding and difficult issues meant it would take time to conclude a deal.