Citizens' protection minister Michalis Chrisochoidis said the extension to the existing 12.5km fence on its border with Turkey is complete and has been fitted with a hi-tech, automated electronic monitoring system.
Greece has completed work on a 40km fence with surveillance system to stop asylum seekers crossing into Europe following the Taliban's takeover of Afghanistan.
Events in Afghanistan have fuelled fears in the European Union of a repeat of the 2015 refugee crisis, when nearly a million people fleeing war and poverty in the Middle East and beyond crossed to Greece from Turkey before travelling north to wealthier states.
Greece was on the frontline of that crisis and has said its border forces are on alert to make sure it does not become Europe's gateway once again.
The Afghanistan crisis had created "possibilities for migrant flows", citizens' protection minister Michalis Chrisochoidis said after visiting the region of Evros on Friday with the defence minister and the head of the armed forces.
"We cannot wait, passively, for the possible impact. Our borders will remain safe and inviolable," he added.
Mr Chrisochoidis said the extension to the existing 12.5km fence on its border with Turkey had been completed in recent days and fitted with a hi-tech, automated electronic monitoring system.
Migrant arrivals to Greece, either by land or by sea, have slowed to a trickle since 2016, when the EU agreed a deal with Turkey to stem the flow in exchange for financial support.
Prime Minister Kyriakos Mitsotakis and Turkish President Tayyip Erdogan discussed Afghanistan on the phone on Friday.
Mr Erdogan said Iran - a key route for Afghans into Turkey - should be supported or a new migration wave was "inevitable", a statement from his office said.
Greece has hardened its migration policy in recent months by fencing off its migrant camps and has revealed plans to build two closed-type facilities to house asylum seekers on the islands of Samos and Lesbos, close to Turkey.
There have been chaotic scenes outside Kabul's airport every day this week as desperate crowds of Afghans try to flee the country.
Currently, there is a race against time to get westerners and their Afghan allies, including translators, interpreters, and other vulnerable people, out of Afghanistan before American soldiers, who are leading the evacuation effort, are due to leave the country by 31 August.
But the Taliban has assured the US they will allow Afghans to leave after 31 August if they wish to do so, according to the US state department.
The UK has committed to taking up to 5,000 Afghan refugees in the first year of a new and separate resettlement scheme, and up to 20,000 in the longer-term.
SOURCE: Sky News
