|Obama has prioritised a reduction in nuclear arms as part of his foreign policy [AFP]
Russia has said that it will not change a draft nuclear arms treaty with the US, that Barack Obama, the US president, wants ratified with Senate support by the end of this year.
On Monday Sergey Lavrov, the Russian foreign minister, said to the Russian news agency Interfax that the proposed New START treaty "cannot be opened up and become the subject of new negotiations".
The treaty is set to reign in Russian and US nuclear arsenals, but needs parliamentary approval in both nations.
Legislators must agree that it will correspond with their national interests, and on Monday Obama attempted to convince reluctant Republican senators to support it.
Obama lobbied senators by phone to ratify the treaty before January, when five additional Republicans take their elected seats in the Senate, which would further endanger the support of the pact.
A vote is to be held on Tuesday in the Senate to stop the debate and hold a final poll to ratify the deal this week.
At least two-thirds of the Senate need to approve the treaty for it to pass, meaning Obama needs Republican support for it.
Its ratification would be a boost for Obama who has prioritised the elimination of nuclear weapons in his foreign policy, while he has faced significant criticism at home on the economy and on health care reform that many see as watered down.
The New START deal would cap nuclear weapons and restart weapons inspections.
Top Democrats, including Joe Biden, the vice president, said they believe they have enough support in the senate to ratify the new nuclear arms treaty.
Biden also told NBC's "Meet the Press" on Sunday that the US would "make good" on its commitment to fully develop a missile defence system in Europe.
Two Republican senators - Scott Brown of Massachusetts and Thad Cochran of Mississippi - have said that they will support the treaty, but Democrats know that its passing is far from certain.
"It's going to be a real slog, house by house combat if you will," New York's Democrat senator Charlie Schumer said on ABC news on Monday.
"But I think we'll be there."
Republicans opposing the treaty say the pact would limit US efforts to develop systems like those it plans to deploy in Europe to defend against any limited missile attacks from Iran or North Korea.