Spain gave the final green light Friday for the US navy to deploy four ships equipped with missile interceptors in its territory as part of NATO's ballistic defence shield.

Equipped with Aegis defence systems, the ships are to be deployed at a US naval base in Rota, southern Spain by 2013, along with 1,400 US personnel, under a deal agreed a year ago, the government said.

The government authorised the signing of the deal under a joint defence agreement at a cabinet meeting on Friday, it said in a statement.

"Its principal activity will be to contribute to defending against ballistic missiles," it said.

Leaders of the 28-member NATO alliance gave their backing in 2010 for the Europe-wide ballistic missile shield -- which US officials say is aimed at thwarting missile threats from Iran.

The system will later expand to include land-based interceptors in Romania, Poland, Turkey and The Netherlands.

Spain's Deputy Prime Minister Soraya Saenz de Santamaria told a news conference that the development of the installations, financed by the United States, would boost the economy in the region, suffering in Spain's recession.

The left-wing political coalition United Left which jointly governs the surrounding Andalusia region along with the Socialists, criticised the decision, however, saying it made Spain "a military target".