Russian Foreign Minister Sergei Lavrov said on Tuesday that a new Russia-U.S. treaty on nuclear arms reduction could be signed within two or three weeks.

However, White House spokesman Robert Gibbs said the same day that Washington did not intend to "rush the negotiations."

These different sayings have indicated that the signing of a replacement document for the Strategic Arms Reduction Treaty (START-1) might still be up in the air.

So what's actually barring the two sides from reaching a deal?

Russia and the United States have been working on a successor to the 1991 START-1 that expired on Dec. 5, 2009.

An outline of the new pact, agreed by Russian President Dmitry Medvedev and his U.S. counterpart Barack Obama, includes slashing nuclear warheads to 1,500-1,675 and delivery vehicles to 500-1,000.

Since May 19 last year, ten rounds of negotiations have been conducted between the two sides. Despite a media highlight, a definitive date for the signing of the new treaty remains undetermined.

According to Russian media, divergences between Moscow and Washington lie in four aspects: number of reductions, delivery vehicles, verification and the linkage between nuclear arsenal cut and missile defense.

Based on recent assurances from the Russian side, analysts said the majority of divergences have probably been solved.

Russia has repeatedly said that the two sides are coming close to reaching a new deal. On Jan. 24, Medvedev said the new arms treaty with the United States was "95 percent coordinated."

On Feb. 24 in a telephone conversation with Obama, Medvedev "stressed the importance of concluding the negotiations in a short term to prepare this document, which is critical to strategic security and stability, for signing as soon as possible."

On March 5 at a meeting with Defense Ministry officials, Medvedev said Russia "managed to come very close to a new nuclear arms reduction treaty that will further cut relevant arms in a relatively short period of time through intensive talks with the United States."

However, on Tuesday White House spokesman Gibbs said: "We are certainly hopeful that that can be done in short order," but "we' re not looking to rush the negotiations in order to ... have a signing ceremony prior to" the Nuclear Security Summit slated for April 12-13 in Washington.

One lingering stumbling block may be the issues concerning missile defense, said analysts.

Russian media have cited sources as saying that Moscow suggested to exchange relevant information in letters, which shall also be included in the new treaty to become legally binding. Washington may not want such inclusion, but would rather take it as a political responsibility.

Russia's top diplomat Lavrov reiterated on Tuesday that the new arms control deal would link strategic offensive and defensive weapons, which was agreed by Medvedev and Obama during their last April's meeting.

"This link will undoubtedly be reflected. It will be documented in a legally binding form," he said.

Therefore it is quite practical to determine the relationship between strategic offensive and defensive weapons, said analysts.

Meanwhile Russia still awaits confirmation and further explanation from the United States concerning its plans to deploy elements of a missile shield in East Europe.

Obama last September scrapped plans for a radar in the Czech Republic and 10 missile interceptors in Poland pursued by his predecessor as a so-called protection against possible missile threats from "rogue states."

In February, however, Romania and Bulgaria angered Moscow by announcing that they were ready to be part of the revamped U.S. missile defense system.

Yet in all, the divergences over the missile defense issue shall not prevent the two sides from reaching the new START deal, as signing the new pact reflected the political will of both countries' leaders, said analysts.

For Obama, inking the deal would indicate the correctness of his policy to "reset" U.S.-Russian relations, as well as his capability to reach agreements with Russia.

For Medvedev, the deal would be the most important one for him to sign since taking office.

Therefore, the new treaty will eventually come to place, said analysts. But only time can tell when that's going to happen, they added.