A massive security exercise is under way in Greece involving troops who will be on hand to protect this summer's Olympic Games.
Security for the Games involves international forces
Code-named Hercules Shield, it involves 1,500 Greek and 400 US soldiers, and international security advisers.
Several scenarios are expected to be enacted, including a "dirty bomb" attack and a ship hijack.
The two-week drill began on the day that the country's new centre-right government was sworn in.
New Prime Minister Costas Karamanlis has pledged to make the Games the "best and most secure ever".
Attacks in neighbouring Turkey have raised concerns that the event could be targeted by Islamic militants.
Under cover of a media blackout, the security exercise is being carried out in Athens, ancient Olympia and four other major cities where sporting events will take place during August's Olympics.
BBC Athens correspondent Richard Galpin says the Greek authorities are training to deal with the possibility of the most catastrophic terrorist attack.
Many Olympic building projects are behind schedule
They say they want to be prepared for anything, as the Olympics will be the biggest international gathering since the 11 September attacks on the United States in 2001.
Our correspondent says the security operation will be the biggest and most expensive in Olympic history and is expected to involve Nato surveillance aircraft and rapid reaction forces in case of an attack.
Fears were heightened last November when suicide bombers attacked synagogues and British targets in neighbouring Turkey, killing more than 60 people.
Mr Karamanlis wasted no time in getting down to business following his New Democracy Party's victory over the socialists in Sunday's elections - the first time a conservative party has been in power for more than a decade.
After a brief swearing-in ceremony at the presidential palace, led by the Archbishop of Greece's orthodox church, Mr Karamanlis held a full cabinet meeting.
The Archbishop of Greece carried out the ceremony
He told his ministers that the government "will have no grace period".
"It's our commitment to act with modesty, with humility, with boldness, with decisiveness with vision, with planning, with optimism and with gusto," he said.
"From today we start work."
Our correspondent says the sense of urgency reflects the pressing issues facing the country.
As well as the Olympic Games pressures - which include the fact that several key building projects are behind schedule - negotiations on the reunification of Cyprus are now at a critical stage.
Athens and Ankara may find themselves directly involved in the talks later this month as called for under the United Nations plan if the Turkish and Greek Cypriot sides are not able to resolve their differences.