Republicans are trying to block Obama administration overtures to Russia on missile defense, creating a potential obstacle to arms control talks.

Lawmakers are proposing a measure that would bar the administration from sharing classified missile defense data with Russia.

That would undercut a path that arms control advocates have urged to restart nuclear talks, which have been set back by a missile defense dispute. They say that if the United States releases classified data, it could persuade Moscow that the system is not targeting Russian missiles.

Republicans are wary of any concessions to Russia and see President Barack Obama as being too weak in negotiations.

The proposal is part of a defense bill that is in its early stages in the legislative process. Its prospects for becoming law are uncertain.