Russia is thinking of aiming nuclear weapons at western Europe for the first time since the end of the cold war, according to defence sources in Moscow.

The move is being considered in response to American plans to develop a defence shield against missiles from Iran and other countries.

The plans under discussion include the possible deployment of ballistic missiles to Kaliningrad, a Russian enclave between the European Union countries of Lithuania and Poland. Kaliningrad has been nuclear-free since America and Russia agreed to scale back their nuclear arsenals at the end of the cold war.

A Russian parliamentary committee visited the enclave 10 days ago to examine how a new generation of nuclear missiles could be based there. Any such deployment would significantly escalate tensions in Europe between Moscow and Washington.

Condoleezza Rice, America’s secretary of state, signed an agreement in Prague last week to build a radar station in the Czech Republic. The station is an important part of the US missile shield. Washington says the shield will defend Europe and America against attacks from rogue states such as Iran and North Korea.

Another deal, for Poland to host a base for 10 interceptor rockets on its border with Russia, is expected to be concluded later this year.

Moscow is bitterly opposed to the shield, saying that it is part of an aggressive US military expansion into its own back yard.

“One of the main steps under consideration is a redeployment of nuclear missiles to Kaliningrad and Belarus,” said a source with close connections to the Russian defence ministry.

“These missiles would be pointed at Europe. It would be a perfectly legitimate step. If America wants to expand its military capabilities in Europe, then we have the right to act accordingly.”

The source disputed America’s claim that the shield was intended to intercept missiles only from rogue states. “How would Washington feel if we placed interceptor missiles on Cuba or Venezuela?” he said.

Experts said the threat of deploying missiles in Kaliningrad was largely aimed at fuelling opposition to the shield in Poland and the Czech Republic, where oil supplies to its refineries from Russia fell sharply last week.

It would require Russia to build new long-range ground-based ballistic missiles since it has destroyed most of its Soviet-era arsenal.

“We take the possibility of missiles being redeployed against Europe very seriously and are aware of the discussions about Kaliningrad,” said a western diplomat. “But we also think there is some bluff involved. The Kremlin is banking on one thing — that the shield won’t see the light of day before President George W Bush leaves the White House next year and it could be scrapped after that.”

Russia’s angry response dispelled any illusion that under Dmitry Medvedev, its new president, the Kremlin would be any less hardline than it was during Vladimir Putin’s presidency. Putin, now prime minister, is widely viewed as Russia’s most powerful man.

Any hope that relations between Russia and Britain, which are at their worst since the end of the cold war, might improve following Gordon Brown’s meeting with Medvedev at the G8 summit last week was short-lived.

On Friday the Russians accused a British diplomat of being a spy. The claim followed accusations in Britain that the Russian state had been involved in the polonium poisoning of Alexander Litvinenko, the former KGB agent, in London in 2006 — which Moscow denies.

The FSB, the former KGB intelligence service, claims British spies are the world’s most aggressive in covert operations against Russia. It also suspects the British Council, a cultural organisation, of being a front for intelligence.

“Britain and Russia are in the middle of an intelligence battle,” the western diplomat said. “New president or not, it will take a long time to repair relations. More cold war spy scandals are very likely.”

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