Obama and Medvedev signed the nuclear treaty in April [AFP]

US president Barack Obama attempts to ratify the START nuclear treaty with Russia by the end of 2010 has suffered a serious setback when a key Republican senator said there was not enough time  to resolve remaining differences.

Kyl, who has been pressing for more funds to modernise US strategic forces, issued a statement on Tuesday, saying he did not believe the outgoing Congress had the time this year to finish its work on the treaty.

The statement prompted Joe Biden, the US vice president, to warn that failure to pass the treaty this year would threaten US national security by leaving the two countries uninformed to each others' nuclear intentions.

Biden said the administration had moved to address Kyl's concerns about nuclear modernisation, making clear it planned to invest $80 billion over the next decade to upgrade US nuclear forces, and pledging an additional $4.1bn for the next five years following consultations with Kyl.

The treaty was signed by Obama and Dmitry Medvedev, his Russian counterpart, in April and committed the former Cold War enemies to cut deployed nuclear weapons by about 30 per cent within seven years.

It must also be approved by the US Senate and the Duma, the lower house of the Russian parliament, before it will enter into force.

Medvedev has pushed the Duma not to ratify the treaty until US Senate approval is certain. It is unclear whether the accord could move to a vote of the full Senate without Kyl's support.

Top priority

Democrats need significant Republican support to gain the 67 votes to ratify the treaty in the 100-member chamber.

Officials have said Kyl is key to approving the treaty this year.

Obama has made ratification of the treaty one of his top priorities for the remaining weeks of the current Congress.

On Sunday, he reassured Medvedev that he was committed to getting Senate approval for the accord by the end of the year.

Democrats fear the treaty will face greater opposition when the new Congress is seated next year because losses in recent nationwide elections left them with only a slim majority in the Senate.

Source: Agencies