Russia said Wednesday it was "no longer bound" by limits on the number of nuclear warheads it could deploy, as its last arms control treaty with the United States looked set to expire. The New START agreement will end Thursday, formally releasing both Moscow and Washington from a raft of restrictions on their nuclear arsenals. Campaigners have warned the treaty's demise could unleash a new arms race between the world's top nuclear powers, and encourage China to expand its arsenal.