The New Start nuclear treaty between the US and Russia has cleared a key procedural hurdle in the US Senate and now looks set to be ratified.
Senators voted to end debate on the issue, clearing the way for a final vote on the treaty, set for Wednesday.
Ratification would be a victory for President Barack Obama and the Democrats, who have pushed hard for it.
Some Republican senators oppose the treaty on a variety of grounds, though Mr Obama has called it crucial.
Treaty 'needed now'
"We are on the brink of writing the next chapter in the 40-year history of wrestling with the threat of nuclear weapons," Senate Foreign Relations Committee chairman John Kerry, a Democrat, said after the vote.
The 67 votes in favour of the parliamentary motion to end debate puts the treaty above the threshold needed for ratification at the final ballot, and Mr Kerry said he expected as many as 70 votes.
"In our nation's security interest we need a New Start treaty now," Republican Richard Lugar told reporters, dismissing the calls from others in his party to hold more hearings next year.
The New Start treaty would trim US and Russian arsenals to 1,550 deployed nuclear warheads - a cut of about 30% from a limit set eight years ago. It would also allow each side visually to inspect the other's nuclear arsenal to verify how many warheads a missile carries.
The previous missile treaty expired more than a year ago, and Mr Obama and Russian President Dmitry Medvedev signed the New Start pact in April.
For the treaty to take effect, it needs the votes of two-thirds of the US Senate, or 67 if all 100 senators are present.
Top Republicans, including Minority Leader Mitch McConnell, John McCain and Jon Kyl, have said they oppose the treaty.
Russian warning
They and other Republicans have lodged several procedural complaints, including an objection to Democratic efforts to hold a vote before the end of the year, and say they oppose non-binding provisions they say would hinder US development of missile defence technology.
Meanwhile, some analysts have suggested Republicans oppose the treaty for political ends, seeking to deny Mr Obama a crucial foreign policy accomplishment.
Russian Foreign Minister Sergei Lavrov has warned the treaty would be scrapped if Republicans succeeded in altering its form from the document signed in April.
On Monday, Adm Mike Mullen, chairman of the US Joint Chiefs of Staff, sent a letter to congressional leaders on Monday urging them quickly to ratify the agreement, becoming the latest in a series of senior military and civilian national security officials to back it.