NEA VYSSA, Greece — Border police jeeps hurtle along hot, dusty tracks past potato fields on their way to the river that marks the Greek-Turkish border. Sirens blaring, the convoys have been repelling wave after wave of migrants.
Greece's remote Evros region has turned into Europe's main battleground against illegal immigration. More than two-thirds of people making the clandestine journey into the European Union pass through here from neighboring Turkey.
Greece launched an aggressive campaign this month to try to seal its 130-mile northeastern border as it faces a debilitating financial crisis that has caused a swell in joblessness and a surge in racist attacks against immigrants with dark skin.
The police operation has brought nearly 2,000 additional border guards to the Turkish frontier previously manned by about 500 officers.
They fanned out with dogs, night-vision equipment and flat-bottomed boats for 24-hour patrols of the Evros River that forms a natural border. At least 21 people have drowned or died of exposure crossing the river this year, while several have been listed as missing.
In Athens, the operation is being bolstered by mass roundups of suspected illegal immigrants. They are seen lined up on the streets of the capital every day, many in handcuffs, waiting to be put in detention until they can be deported.
In the first week of the crackdown in early August, police said they apprehended nearly 7,000 people for identification checks. Nearly 1,700 were slated for deportation.
Gaming the system
Anwar, a 22-year-old man from Bangladesh, walked across the border near Orestiada, a small town wedged between Turkey and Bulgaria.
Unaware of the immigration clampdown, he said he is looking for police so he can turn himself in. It's a well-worn ploy: Migrants have actively tried to get themselves taken to detention centers near Athens, assuming they will be released because of overcrowding and allowed to blend into the chaotic capital.
"I've come here to work," Anwar, who declined to give his full name because of his illegal status, said moments after crossing the border.
"I know what will happen to me: They might keep me in detention for around three months, but then they'll let me out and I'll go to Athens."
Now, however, authorities are determined to deport swiftly any illegal migrants they round up.
In a recent pre-dawn operation, authorities using thermal-imaging cameras spotted a group of about 60 people on the Turkish side of the Evros River.
Officers used spotlights, sirens and loud speakers to deter them from crossing, although 15 still made it over to a river islet in a no-man's land and were arrested.
Uniformed police officers from 25 countries are helping Greece guard the Evros River as part of the European Union's border protection agency, Frontex.
According to Frontex estimates, 21,000 immigrants and asylum seekers managed to cross over illegally in the first six months of 2012.
Afghans currently make up the highest number of people crossing illegally, followed by Pakistanis, Bangladeshis, and an increasing number of people from war-ravaged Syria, according to the agency.
Human rights groups object
The police operation has faced strong criticism from human rights groups, local officials, and even police officers' associations -- with criticism focusing on alleged racial profiling and police brutality.
Police video showing riot police and other officers rounding up mostly South Asian immigrants as they got off a train that arrived at Athens' main station also received condemnation from local rights groups and left-wing opposition parties.
Amnesty International called on Greek authorities to stop the roundups immediately.
"While Greece has the right to control migration, it does not have the right to treat people like criminals purely because of the color of their skin," Amnesty's Jezerca Tigani said in a statement.
He warned that many immigrants fleeing war zones and potential persecution from dictatorial regimes are being denied a fair asylum assessment.
"Greece may be going through financial difficulties while facing one of the highest migration flows among EU countries," Ms. Tigani said, "but these police operations violate international human rights standards and should stop immediately."
Police say migrants' rights are being respected.
"Our aim is to deter illegal immigrants and arrest traffickers, but the migrants' well-being and rights are always a main priority," said Orestiada police Chief Yiorgos Salamangas.
The government insists the operation is working. It reported a drop in illegal border crossings by about 90 percent in the first week.
"This is a massive operation that is taking place in the country for the first time, and it will continue in the long-term," police spokesman Christos Manouras said.
"It is widely accepted that the expulsion of immigrants who are here illegally is a national necessity, an issue of national survival."
Greece is a member of Europe's passport-free Schengen agreement but shares no borders with any of the other 25 nations that signed the treaty.
That has meant hundreds of thousands of irregular immigrants have been unable to cross the border into other European countries, trapping them in limbo in Athens and other Greek cities, typically in slum conditions.
As the country struggles through a fifth year of recession, illegal immigration and a rise in violent crime have become central issues in the political debate. Mainstream parties blamed by many for the country's near financial collapse face opposition from more radical political groups.
The extreme right Golden Dawn party, described by political opponents as neo-Nazis, won nearly 7 percent of the vote in June general elections, a 20-fold jump since a national vote in 2009.
The party denies any involvement in a recent surge in anti-immigrant attacks and says police should be more concerned by attacks on Greeks by foreign criminals.
In one suspected attack by racist gangs this month, an Iraqi man was stabbed in the street and died hours later in a hospital.
Anti-racism campaigners last month said immigrants living in Greece were targeted in at least 300 violent attacks from early April to late July. The rise in hate crimes is believed to be one of the triggers of the government clampdown.
Authorities are using a newly built detention center near Athens and two converted police academy buildings in northeastern Greece to house detainees, while dozens more facilities are planned using converted military bases.
Police associations argue that the massive deployment of manpower should have been delayed until more of those new facilities are ready. They cite the lack of detention capacity as a key reason for the country's inability to deal with illegal immigration.
It's a concern shared by local authorities in the Evros region, and many residents.
"As long as people know they can make it here and eventually live freely, they will keep coming," said Christos Kyriakidis, 63. "Nothing will stop them."