Russian President Vladimir Putin has announced what he called a vast programme to upgrade the country's missile defence system.
The new radar station was built in just 18 months
Visiting a new radar early-warning station near St Petersburg, Mr Putin said it was the first step in a major construction project lasting till 2015.
Russia has grave concerns about plans to deploy parts of a new US missile defence system in Eastern Europe.
Mr Putin has warned that Russia will take measures to counter the plan.
The US insists its programme is aimed to deal with threats from countries such as Iran and North Korea, and says Russia should have nothing to fear.
Russia has offered a compromise solution, which would allow the US to share use of a radar installation in Azerbaijan.
Mr Putin described the new early-warning station - at Lekhtusi, 50km north of St Petersburg - as "the first step in the implementation of a major early-warning programme up to the year 2015".
The station was built in just 18 months and opened in December last year.
It replaces the Soviet Union's Skrunda radar station in Latvia, which was dismantled in 1998.
A similar installation is under construction at Armavir in southern Russia.