The leaders of Russia and the United States said Sunday they were on target to agree by the end of the year the text of a new treaty setting out major cuts in their nuclear weapons arsenals.
But a senior White House adviser warned there was not time for the successor to the 1991 START agreement to be ratified by December 5 when the old treaty elapses, meaning a temporary bridging deal would be needed.
"I expect that we can have a final text of the agreement by December," Russian President Dmitry Medvedev said after talks with his US counterpart Barack Obama on the sidelines of an Asia-Pacific summit in Singapore.
Obama said: "Our goal continues to be to complete the negotiations and to be able to sign a deal before the end of the year.
"I'm confident that if we work hard and with a sense of urgency about it that we should be able to get that done." Medvedev said there were "technical" issues that needed to be resolved on the agreement, which will take over from the Strategic Arms Reduction Treaty (START) that was signed just before the collapse of the Soviet Union.
"We agreed to give an extra dynamic to these talks to find solutions to outstanding questions," Medvedev said after the conclusion of the two-day Asia-Pacific Economic Co-operation (APEC) forum in Singapore.
"In some cases these are technical questions, in other cases these are questions which demand political decisions." Russian officials have insisted the treaty must establish a link between missile defence systems and strategic arms and have also expressed concern about the number of "carriers" that can deliver nuclear warheads.
Russia also does not want the new treaty to require US inspections of its mobile ground-base intercontinental ballistic missiles - as was the case under START - saying this is unfair as the US does not possess such systems.
US and Russian experts have been holding almost non-stop closed door talks in Geneva to agree on every detail of the new document. White House advisor Mike McFaul said that while an agreement was expected in December, it could not be ratified by the legislatures in both countries by December 5 when START expires.
"What I do know for sure is that we will not have a ratified treaty in place by December 5. It still has to go through the US Senate and the Russian Duma," he told reporters.
"What is for sure is that we do need a bridging agreement," he said, adding this was being worked on in the talks in parallel to discussions on the main treaty.
During a visit by Obama to Moscow earlier this year, the two presidents called for a reduction in the number of nuclear warheads in the Russian and US strategic arsenals to between 1,500 and 1,675 within seven years.