NATO has voiced "serious worries" about Russian plans to place short-range missiles on its western border if Washington proceeds with its missile defence systems in Eastern Europe.

A spokesman for the North Atlantic Treaty Organisation, Robert Pszczel, said the alliance had concerns about the compatibility of the Russian plans with arms control "arrangements".

"Moreover, placing of these Iskander missiles in the Kaliningrad region would not help NATO and Russia to improve their relationship," he said.

The plans to deploy missiles on the doorstep of the EU were announced by the Russian President, Dmitry Medvedev, during his first state of the nation address on Wednesday.

The Czech foreign ministry described the announcement as "unfortunate", but the Polish Prime Minister, Donald Tusk, said it should be seen more as a political message.

"In the event that the situation gets bad, the balance of power is already well known," Mr Tusk said. "So we should consider the announcement as a new political step, not a military one."

Kremlin officials have threatened before to target Poland by moving tactical missiles into the Baltic enclave of Kaliningrad, most recently after Poland agreed in August to host a US interceptor base.

But Mr Medvedev's threat "to neutralise, when necessary" the American installation was the most explicit and public endorsement of the plan by a top Russian leader yet.

The warning appeared intended to signal the Kremlin's priorities to the new US president-elect and could serve as an early foreign policy test for Senator Obama, who has said he supports missile defences against Iran and North Korea but has criticised the Bush Administration for failing to consult allies about the shield, exaggerating its capabilities and rushing deployment for political purposes.

If the US president-elect dumps the project he risks accusations of weakness and caving in to Russian bullying.