Russia believes that the new U.S. plans to deploy ship-based interceptor missiles in Europe and later mobile land-based interceptors on the continent may never be realized, a Foreign Ministry spokesman said on Thursday.

In September U.S. President Barack Obama cancelled plans to place 10 long-range ground-based interceptor missiles in Poland and a fixed radar in the Czech Republic. Due to a re-assessment of the threat for Iran, Washington announced a new scheme for a more flexible system, with a combination of land and sea-based interceptors based on the Standard Missile interceptor, SM-3.

Under the new plan, the U.S. would place ship-based SM-3s in the North and Mediterranean seas in 2011, and mobile land-based SM-3s in Central Europe by 2015.

In contrast to the previous system which was strongly opposed by Russia, the new multi-directional radars and missiles would not be able to penetrate deep into Russia's territory. However, Russian officials have voiced concerns over the new plans.

Russian Foreign Ministry Spokesman Andrei Nesterenko said: "Our understanding is that the United States plans to start gradually deploying missile defense elements in Europe that will be adjusted to counter a genuine missile threat."

On the planned scheme for deploying sea-based then land-based SM-3s, he said: "We do not think that the transition from one stage to the other is inevitable."

Nesterenko said the land-based defenses may prove unnecessary by the planned date of 2015.

Polish Prime Minister Donald Tusk said on Wednesday after talks with visiting U.S. Vice President Joe Biden that Poland was ready to take part in the reconfigured U.S. missile defense system.

His statement came a day after Prague said it expected the U.S. to present new specific U.S. missile defense proposals for the country.

Nesterenko said any missile defense configuration in Europe "must be based on joint assessments of real threats."