Russia's foreign ministry voiced its concern Friday at Romania's plans to host part of a new US missile shield system in Europe, saying it would seek explanations from Europe and Washington.

"This is a serious matter which we will be analysing with care," the ministry said in a statement. "Naturally, we are concerned by this. There is a need to obtain clarifications.

"We will raise this in our contacts with our American and European partners," it added.

Romania's President Traian Basescu on Thursday announced his country had agreed to host medium-range ballistic missile interceptors as part of the US system, expected to be operational by 2015.

The US State Department confirmed his announcement, saying the planned anti-missile shield in Europe was intended to protect against the "emergent threat" from Iran.

The United States in September shelved a plan to place missile defense facilities in the Czech Republic and Poland, after strong protests from Russia.

President Barack Obama's administration announced the new program in September, saying it would reconfigure the system after reevaluating the threat from Iranian long-range ballistic missiles, and deciding to focus on protecting against short- and medium-range missiles.