The plans to share unspecified “secret data” on the missile defense shield with Russia were first voiced late last week by Bradley Roberts, U.S. Deputy Assistant Defense Secretary. Pentagon spokeswoman April Cunningham confirmed this information for a Kommersant newspaper article published on Monday.

It is not yet clear exactly which data may be disclosed to Russia, which has for years strongly opposed American plans to deploy a missile defense shield in Eastern Europe, including Poland, Romania and the Czech Republic.

The White House insists the program is aimed against a potential threat from rogue states such as Iran and North Korea but Russia says its own missiles will also fall under the shield, destroying the nuclear balance that existed since the Cold War.

In November, news leaked that the White House was in secret talks with Russia about providing it with information on the velocity burnout of the modified version of the SM-3 rocket, which is to become the staple interceptor rocket of the U.S. missile shield by 2020. However, the U.S. administration denied at the time that it proposed to disclose the data on the rocket’s crucial parameter to Moscow.

“If they are really going to disclose data on [rocket] speed, that’ll be the decisive argument” for Russia, said Alexander Khramchikhin, a researcher with the Moscow-based Institute for Political and Military Analysis think-tank.

Speed of interceptor rockets is the only thing the Russian military needs to know to determine whether the U.S. missile shield really poses a risk to Russian rockets, Khramchikhin said by phone on Monday.

The move would be unprecedented but not impossible, though the upcoming U.S. presidential campaign is likely to hurt these plans, said Khramchikhin. Republican opponents of incumbent President Barack Obama, who is planning to seek reelection, have repeatedly accused him of being too soft in his dealings with Russia.

Russian officials have not commented on the proposal as of Monday.

Russian-American talks on the missile defense shield failed to progress last year, with both sides refusing to make any significant concessions. However, the matter is to be taken up again in May at an international conference in Moscow organized by the Russian Defense Ministry and a NATO summit in Chicago later the same month.