A major nuclear arms reduction deal between the US and Russia seems to be in danger of collapse after an influential Republican senator said it should not be voted on this year.
Jon Kyl's remarks were a major setback to President Barack 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 Mr Obama's top foreign policy accomplishments.
Without the support of Mr 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.
Mr Kyl's position, unless reversed, will delay the vote until the newly elected Senate, with an expanded Republican minority, has been sworn in 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.
Following the 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 US authority that expired last year to inspect Russia's nuclear arsenal.
Chairman of the Senate Foreign Relations Committee, Democrat John Kerry, said he had discussed the issue with Mr 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.
Mr 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 US and Russian limits on strategic warheads to 1,550 for each country from the current ceiling of 2,200. Republicans have argued that the treaty would limit US missile defense options and does not provide adequate procedures to verify that Russia is living up to its terms.
Mr Kyl has argued that it makes no sense to reduce the number of US warheads until more is done to maintain and modernise the remaining arsenal. Last week the administration sought to satisfy Mr Kyl's conditions for supporting the treaty with a proposal to boost funding significantly for the US nuclear weapons complex.