U.S. President Barack Obama said Thursday that it was a "national security imperative" for the Senate to ratify a new nuclear reduction treaty with Russia this year.

Obama made the remarks at a meeting at the White House on why the new Strategic Arms Reduction Treaty (START) he signed in April with Russian President Dmitry Medevedev is in U.S. national security interest.

"It is a national security imperative that the United States ratify the new START treaty this year," Obama stressed at the meeting chaired by Vice President Joe Biden, joined by current and former high-ranking officials who support the treaty, including former secretaries of state Madeleine Albright, James Baker and Henry Kissinger and former defense secretaries William Cohen and William Perry.

Obama added: "This is not about politics, it's about national security. This is not a matter that can be delayed."

The new START treaty is seen as a major achievement of the Obama administration in foreign relations and part of its efforts to reset relations with Russia.

Obama reiterated to Medevedev on Sunday that it is a "top priority" of his administration to get the U.S. Senate to ratify the new START pact, which stipulates that the number of nuclear warheads be reduced to 1,550 on each side over seven years, while the number of delivery vehicles, both deployed and non-deployed, must not exceed 800.

The U.S. Senate Foreign Relations Committee approved in September the new START treaty, clearing the way for a vote on the Senate floor. The U.S. and Russian presidents had agreed that the ratification process should be simultaneous at U.S. Senate and Russia's Duma.

Some Republicans have been blocking the treaty, saying it would prevent the U.S. from maintaining and modernizing its nuclear stockpiles, among other things. To assuage their concerns, Obama has promised an extra 4.1 billion dollars in addition to an existing 80 billion dollar over 10 years for the modernization of the country's nuclear weapons complex.

However, Republican Senator Jon Kyl, who is seen as key to winning enough support to ratify the treaty, said Tuesday that a deal did not seem possible in the lame-duck session.

Obama's Democrats lost control of the House of Representatives to the opposition Republicans in the Nov. 2 mid-term elections but retained control of the Senate. On Monday, a lame-duck session of Congress begins until the start of the new Congress in January next year, where lawmakers who have been voted out of office attend the session while those newly-elected do not.

In the United States, the lame-duck session is a time for the governing party to try to act on stalled bills. This period is sometimes productive as those outgoing lawmakers oftentimes vote with a free hand.

"There is no higher national security priority for the lame- duck session of Congress," Obama said at the Thursday meeting. " The stakes for American national security are clear, and they are high. The new START treaty responsibly reduces the number of nuclear weapons and launchers that the United States and Russia deploy, while fully maintaining America's nuclear deterrent."

He added: "If we ratify this treaty, we're going to have a verification regime in place to track Russia's strategic nuclear weapons, including U.S. inspectors on the ground."

"I'm confident that we should be able to get the votes," the president said.

For the passage of the treaty in the Senate now, the Democrats need nine Republican votes for support. If delayed until next year when the new Congress opens, 14 votes are needed.

U.S. Secretary of State Hillary Rodham Clinton, who represented New York State in the Senate before she quit the post to join the 2008 presidential race, is expected to use her relations in the Senate to get the treaty to pass.