The United States and Russia are within sight of a new deal to slash their nuclear arsenals but certain "principles and elements" have yet to settled, a top US official said Wednesday.

"We are at the end game -- we see the finish line -- of negotiations in the START follow-on treaty," US undersecretary of state for arms control Ellen Tauscher told a conference on nuclear deterrence in Washington.

"There are principles and elements that are still yet to be finished in these negotiations. But I am confident that the teams are working hard and the finish line is within sight."

Russia's ambassador to the United States, Sergei Kislyak, who addressed the conference after Tauscher, said he agreed with "almost each and every word" that she had said about the state of the negotiations in Geneva.

"Mind you, the closer you come to the endgame the bigger each and every small detail becomes," he added.

The upbeat assessments were echoed in Moscow by the head of the Russian armed forces, General Nikolay Makarov.

"The accord is 97-percent finalized by the parties. Some technical issues remain which will be resolved very soon," Makarov said, according to Russian news agencies.

Negotiations on a replacement to the 1991 Strategic Arms Reduction Treaty (START), which expired December 5, have dragged on for months despite periodic reports that the two sides were near agreement.

The White House denied last week that differences with Russia on US missile defense plans in Europe were the reason for the delay.

But Kislyak said US missile defense plans for Europe were a source of uncertainty for Russia despite a more "reassuring" stance taken by President Barack Obama, who shelved plans for a radar and long-range missile interceptors.

"Now we are working on the issue of reducing nuclear weapons in an environment where the United States is introducing anti-ballistic capabilities," the ambassador said.

Citing reports from Bulgaria and the Czech Republic of new missile defense sites there, he said "we are not sure we fully understand how things are working out."

"We are not sure that the story we are hearing is the story that is going to develop within the timespan of the would-be treaty -- that is ten years," he said.

Tauscher said the latest US plan for phased deployments of medium and short-range interceptor missiles over the next decade in Europe was aimed at stopping missiles coming out of the Middle East, not Russia.

"We've not made an offer to Bulgaria about hosting any element of the phased adaptive approach," Tauscher said.

The plan calls for deployment of sea-based SM-3 interceptor missiles on ships in the Mediterranean next year, ground-based SM-3 interceptor missiles in Romania in 2015, and ground-based SM-3 interceptor missiles in Poland in 2018. Upgraded missiles would be deployed in 2020.

The broad outlines of a new treaty on nuclear weapons have been clear since a summit in July, when President Barack Obama and his Russian counterpart Dmitry Medvedev agreed to slash the number of warheads on either side to between 1,500 and 1,675.

The presidents also agreed that the number of carriers capable of delivering the warheads should be limited to between 500 and 1,100.

The United States has said it currently has some 2,200 nuclear warheads, while Russia is believed to have about 3,000.