There has been a drop in the number of immigrants trying to enter Greece illegally and a rise in the amount trying to leave the country over the past few days, authorities said on Wednesday, as human rights groups slammed the government for its latest crackdown on illegal immigration.

The police launched on Saturday an operation aimed at detaining and deporting undocumented migrants, particularly in central Athens. By Wednesday, some 2,000 people had been detained as part of the “Xenios Zeus” initiative.

However, the operation drew strong criticism from Amnesty International, which asked for Greece to halt the process. “While Greece has the right to control migration, it does not have the right to treat people in the street like criminals purely because of the color of their skin,” said Jezerca Tigani, deputy director of the Europe and Central Asia Program.

“The scale of the police operation in Athens at the weekend raises serious concerns about discrimination on the basis of perceived ethnicity,” she added.

Tigani said that the police operation could fuel further attacks on migrants. She also called on Greek authorities to improve access to asylum.

Another group, Human Rights Watch expressed similar concerns. “Greece has the right to enforce its immigration laws… but it doesn’t have the right to treat people like criminals or to presume irregular immigration status just because of their race or ethnicity,” said Benjamin Ward, deputy director of the Europe and Central Asia division.

HRW also drew attention to the rise of far-right Golden Dawn and frequent attacks on migrants. “Police inaction is the rule,” said the group. “These sweeps are a dangerous distraction from the real policing challenges the country faces,” added Ward.

Authorities in western Greece said they have arrested over the past few days dozens of migrants trying to leave the country with fake documents via the port of Patra and airports of Araxos and Aktio. They believe trafficking gangs are stepping up their efforts to move immigrants on to other countries and boost their earnings in the process.

Officials told Kathimerini that in Evros, where some 1,800 extra border guards were put on duty a few days ago, there has been a drop of more than 50 percent in the number of migrants crossing into Greece. A total of 155 arrests were made on Sunday.