A Senate vote on a new U.S.-Russian nuclear weapons treaty seems unlikely this year despite President Barack Obama's assurances to President Dmitry Medvedev that it was a "top priority."

Obama's plans were set back Tuesday when Sen. Jon Kyl, an influential Republican on this issue, said that the pact to slash U.S. and Russia nuclear arsenals should not be voted upon this year.

The terse statement by the Arizona senator dealt a major blow to Obama's efforts to improve ties with Russia and to his broader strategy for reducing nuclear arms worldwide. The treaty, known as New START, had been seen as one of the president's top foreign policy accomplishments.

Without the support of Kyl, the leading Republican voice on the treaty, Democrats have little hope of securing at least eight Republican votes — the minimum they would need for ratification in the current Senate.

Kyl's statement caused a stir in the administration, and Secretary of State Hillary Rodham Clinton scheduled a news conference later Wednesday on Capitol Hill with Sens. John Kerry, D-Mass., and Richard Lugar, R-Ind., the Democratic chairman and ranking Republican, respectively, on the Senate Foreign Relations Committee. They were poised to appeal anew for action in the current lame duck session on the treaty.

On the sidelines of the summit of the Asian-Pacific Economic Cooperation (APEC) last weekend, Obama told Medvedev in a meeting that he believed the treaty could be cleared by the Senate before it leaves for the year.

In Moscow Wednesday, Russia's Deputy Foreign Minister Sergei Ryabkov said officials there still expect the Senate to find time for ratifying the treaty this fall.

"We expect that they will find time to discuss the START ratification package and that the vote will take place during the current session," Ryabkov said, according to the Interfax news agency.

"We have taken note of Senator Kyl's comment. It's not our business to interfere in the procedure of agenda agreement and the Senate's work," Ryabkov said. He added that Moscow is aware that the Senate is facing a busy agenda but still hopes that it will find time to take up the treaty before the year's end.

Ryabkov refused to say what could be the possible consequences of the Senate failing to ratify the treaty this year. "I wouldn't like to theorize. That would not be the best outcome of the work we have done."

He added: "I would like to remind you that the Russian leadership's line that the ratification processes in Russia and the U.S. should be synchronized remains fully valid."

Unless reversed, Kyl's position would delay the vote until the newly elected Senate, with an expanded Republican minority, has been sworn in January. Democrats would then need the support of at least 14 Republicans.

The White House has been trying to avoid that fate, knowing that ratification could slip out of reach in the face of opposition to the treaty from most Republicans and an increasingly partisan political environment in Washington.

At a minimum, that probably would set the treaty back for months, because Republicans are likely to demand new hearings in the Senate Foreign Relations Committee so that newly elected lawmakers would be briefed.

Following Tuesday's setback, Vice President Joe Biden warned that failure to approve the treaty this year would endanger national security. He pointed out that the treaty would renew U.S. authority that expired last year to inspect Russia's nuclear arsenal.

Senate Democrats were holding out hope. Kerry said he had discussed the issue with Kyl and believed the door was still open to a vote before the end of the year.

"Ratifying New START is not a political choice, it's a national security imperative," he said.

Kyl's statement, however, appeared to leave little room to resolve the issue quickly. He said he told Senate Majority Leader Harry Reid that he did not believe the treaty could be considered this year.

The treaty would reduce U.S. and Russian limits on strategic warheads to 1,550 for each country from the current ceiling of 2,200. It also would set up new procedures to allow both countries to inspect each other's arsenals to verify compliance.

Republicans have argued that the treaty would limit U.S. missile defense options and does not provide adequate procedures to verify that Russia is living up to its terms.

Kyl has argued that it makes no sense to reduce the number of U.S. warheads until more is done to maintain and modernize the remaining arsenal.

(This version CORRECTS Replaces 2nd paragraph to correct spelling of Kyl's first name. Will be updated.)