Thousands of migrants are being held in detention centres near Athens before being deported back to their home countries

Greek authorities have begun one of the country's biggest crackdowns yet on suspected illegal immigrants, deploying 4,500 police around Athens and detaining more than 7,000 immigrants in less than 72 hours.

Most have been released, but about 2,000, mostly Africans and Asians, were arrested. They were sent to holding centres pending deportation in an operation that officials, bizarrely, elected to call Xenios Zeus after the Greek god of hospitality.

On Sunday, 88 undocumented Pakistanis were put on planes, accompanied by guards, back to their home country.

"We will not allow our towns, or our country, to be occupied and become a migrant ghetto," said Athens' hardline public-order minister, Nikos Dendias, as authorities discussed plans to build eight detention centres capable of holding up to 10,000 immigrants, in the capital.

Widely seen as the easiest entry point to the west, Greece has had a surge of new arrivals, with government figures showing more than 100 migrants daily crossing the country's porous border with Turkey. The majority go to Athens, a magnet for migrants desperate to find work before moving on to other parts of Europe. An estimated million immigrants are believed to live in Greece where the population is barely 11 million.

But the country's economic crisis and growing political radicalisation has given rise to a xenophobic backlash, the uncontrolled influx blamed for a sharp spike in violent crime.

The neo-Nazi party Golden Dawn, which has vowed to rid Greece of "migrant scum", has seen its popularity soar with the party capturing an unprecedented 6.9% of the vote in parliamentary elections six weeks ago.

Racist attacks by black-clad men associated with extremists have escalated dangerously, according to a recent report by Human Rights Watch.

On Tuesday anti-immigrant fervour grew following the prosecution of a Pakistani who appeared in court accused of assaulting a teenage Greek girl on the Cycladic iIsle of Paros.

In this atmosphere Athens' fragile conservative-lead coalition has taken action. Dendias described the problem of immigrants as "perhaps even bigger than our financial one".

"The country is being lost," he told Skai TV. "What is happening now is [Greece's] greatest invasion ever. Not since the Dorians invaded some 3,000 years ago has it received such a flow of immigration."

Defending the crackdown, he insisted it was imperative to preventing the debt-stricken nation sliding into further chaos and collapse. "Our social fabric is in danger of unravelling," he said.

In the coming weeks arrested migrants would be put in a detention centre outside Athens and unused police academies in the north of the country before being deported, he added. Immigrants were often living in such appalling conditions it was "to their benefit to be repatriated".

On Tuesday Walid Omar, an Iraqi Kurd, was sitting in an internet cafe in Athens' historic city centre when a policeman walked in. The migrant knew the officer well. As a friend of the cafe owner, Omar regularly stopped by and the policeman did too.

But the officer was unusually terse. "He told me and everyone else who did not look Greek to follow him. For the next two hours we were made to wait in a windowless bus, and then under the sun, before they first inspected our clothes and then inspected our papers at the police station," said the Iraqi Kurd whose documents proved he was legal in the country that has been his home for the past 15 years.

"The whole procedure took around five hours and there was a lot of shouting," he continued in fluent Greek. "An Algerian, a young boy, was badly beaten in front of everyone. People were really scared."

Officials said the campaign, which has coincided with the reinforcement of patrols along the Greek-Turkish border, had been also prompted by fears of a new influx of immigrants from Syria.

For the most part the media has welcomed the move with the Kathimerini newspaper opining on Tuesday that security was finally "returning to the centre of Athens".

But the scale of the operation has prompted widespread criticism. The left-wing main opposition Syriza party called the crackdown "a pogrom" and "insult to justice and humanity". Migrants, it said, were being used to divert attention from unpopular economic policies, including more savage spending cuts, demanded by the EU and IMF in return for much needed rescue funds.

"It is a communications stunt aimed at concealing the true crackdown against public-sector wages, pensions and benefits that the government has agreed to in recent days."

The Greek office of the UN High Commissioner for Refugees expressed fears that refugees from war-torn countries and genuine asylum seekers could be among those summarily deported.

Since the start of the year 8,000 migrants have voluntarily sought repatriation, with Greece's situation, economically, socially and politically, having become ever more inhospitable towards them.