Russian President Vladimir Putin says US plans for a missile shield could precipitate a situation similar to the Cuban missile crisis of the 1960s.

Putin was speaking after a summit with EU leaders in Portugal aimed at deepening ties despite disagreements over human rights and foreign policy.

Russia has long opposed US plans to build missile bases in European states once in the Soviet sphere of influence.

The Cuba crisis saw the Soviet Union and US go to the brink of nuclear war.

The 1962 stand-off was triggered when US spy planes discovered Soviet missile bases in Cuba, within striking distance of the American mainland.

Moscow's decision to deploy these weapons in Cuba was at the time seen as a response to the build-up of powerful US missiles in Europe.

Tensions were only defused when Soviet leader Nikita Khrushchev agreed to dismantle the bases in return for guarantees that Washington would not attack communist Cuba.

US President George W Bush has said there is a "real and urgent" need for a missile shield in Europe as a defence against possible attack by Iran and countries in the Middle East.

His defence secretary suggested this week that the development of the bases in countries such as the Czech Republic and Poland could be slowed while Russian concerns were addressed.