Chief of General Staff Nikolai Makarov was quoted as saying that "a decision to use destructive force preemptively will be taken if the situation worsens".
According to an agreement signed last September, he US will place a land-based SM-3 ballistic missile defence system in southern Romania, in the village of Deveselu, Olt county. The military installation is situated around 70 kilometers away from the Bulgarian nuclear power station of Kozloduy.
At a conference in Moscow, computer modeling was used to show how Russia believed the shield could threaten its security.
But NATO's Secretary-General Anders Fogh Rasmussen appeared to de-dramatise the situation, saying that the Alliance was hopeful of reaching a deal with Russia on the matter.
The dispute has slowed improvements in Russian-US ties and is likely to remain an irritant after Vladimir Putin returns to the Kremlin next week for a six-year presidential term.
Washington says the missile defense system, due to be completed in four phases by roughly 2020, is meant to counter a potential threat from Iran. Moscow says the system will undermine Russia's nuclear deterrent because it could also give the West the ability to shoot down Russian missiles.
Rasmussen made his remarks after talks in London on Thursday (3 May) with British Prime Minister David Cameron. Asked whether an agreement could be reached with Moscow, he said: "I'm hopeful that we can."
The Secretary-General said a deal would not happen before a NATO summit in Chicago on 20-21 May.
"We will continue our dialogue with Russia...after the Chicago meeting," he told reporters.
The shield's first phase is to be declared up and running at the summit.
Russia and NATO agreed in 2010 to seek ways to cooperate on missile defense but have failed to reach a deal. The Kremlin wants a legally binding guarantee the system will not be used against Russia. The United States says it cannot agree to any formal limits on missile defense.
The planned system will include interceptor missiles based in Poland and Romania, a radar system in Turkey and missile-defense capable warships at sea.
At the conference in Moscow, Russia's armed forces chief of staff, General Nikolai Makarov, told delegates the system will have the potential to intercept Russian IBMs and submarine-launched strategic ballistic missiles by 2017-18.
The audience, including US and NATO officials, were shown computer-generated images depicting the reach of radars and interceptor missiles to be deployed as part of the shield.
Dome-like designs displaying interceptor ranges and blips of light representing Russian missiles headed for US cities lit up the screen.
A deputy to Makarov, General Valery Gerasimov, said the computer modeling showed that the interceptors would, in several years, be capable of hitting Russian missiles.
He repeated the steps Russia has said it would take if it feels sufficiently threatened by the shield, including what he called an "extreme measure" - targeting the missile installations in Europe that will be part of the system.
US and NATO officials disagreed with the hi-tech presentation and said the anti-missile system would not undermine Russia's security.
"I must say that I am not convinced," said NATO Deputy Secretary-General Alexander Vershbow, a former U.S. ambassador to Russia.
He said the NATO interceptors would be "simply in the wrong place" geographically to counter Russian missiles.
Madelyn Creedon, US assistant secretary of defense for global strategic affairs, said the shied cannot intercept Russian missiles targeting the United States.
"The Russian strategic deterrent is now, and will remain, secure," she said.
Ellen Tauscher, the US special envoy for strategic stability and missile defense, said no deal was likely this year because of the US presidential campaign and possible new administration.
"It's going to be a deal at the presidential level, so I think it's going to be sometime hopefully next year," she told reporters at the conference. "But in the meantime, we've got a lot of work to do to dispel the mistrust."