Dozens of Patriot missiles have been put in place around Athens as the Greek capital began rolling out its security operation for next month's Olympics.
Security is tight in Athens ahead of the Olympic Games
Anti-aircraft missiles are in place at three Athens sites, including Tatoi airfield near the athletes' village, and elsewhere around Greece.
It is part of a 1.2bn-euro security plan ($1.bn), the most costly in the history of the games.
Hundreds of surveillance cameras are also being installed around Athens.
The Greek authorities said the US-made Patriot missiles were progressively installed from 1 July, and would remain in place until after the games end on 29 August.
Three police helicopters and a Zeppelin airship, also equipped with surveillance cameras, will operate almost around the clock during the Olympics, a police source told Reuters news agency.
Patriot missiles and other anti-aircraft devices will also positioned at other cities in Greece.
Russian-made S 300 anti-aircraft missiles are protecting the
city of Heraklion on the southern island of Crete, Greek
Air Force spokesman Constantinos Prionas told AFP news agency.
The Associated Press said Patriot missile sites were also being installed in the northern city of Thessaloniki and one on the Aegean Sea island of Skyros.