In his annual state of the nation address, Medvedev called for closer cooperation with the United States and the European Union, holding out the prospect of closer ties two decades after the Soviet Union's collapse ended the Cold War.

He said tension would ratchet up fast, forcing Russia to bolster its military arsenal, if Western offers of cooperation on a system to defend against missile threats failed to produce a concrete agreement.

The warning appeared to reflect wariness in the Kremlin over uncertainty about Senate ratification of New START, the nuclear arms limitation pact Medvedev signed with President Barack Obama in April, centerpiece of the push for better ties.

The remarks, in a 72-minute speech to members of parliament and ministers, raised the stakes in sensitive discussions with the United States and NATO on missile defense. The issue has divided Moscow and the West since the 1980s.

Medvedev agreed to NATO's offer of missile defense cooperation at a summit with the alliance that was hailed as a fresh start, but the plans are sketchy and Russia has warned it wants an equal voice in evaluating threats and responses.