The chartered flight landed at the Benazir Bhutto International Airport around midday but officials refused to allow 30 of the 49 passengers to disembark, saying their identities had not been confirmed and they therefore could not be repatriated under a 2010 agreement between the EU and Pakistan.
The plane was sent back to Athens around three hours later, according to airport authorities, after 19 of the deportees were allowed to enter the country.
Islamabad had temporarily suspended its agreement with the EU to accept the repatriation of illegal Pakistani migrants citing its “blatant misuse”, saying member countries were not adequately checking the nationality of the deportees.
The deal was restored last week following a meeting between Pakistani officials and EU migration chief Dimitris Avramopoulos.
But Pakistani authorities complained that Thursday’s flight failed to adhere to the terms of the agreement.
“30 unverified deportees arrived at Islamabad from Greece via a chartered plane. On the instructions of the interior minister, the Federal Investigation Agency (FIA) stopped these illegally sent people including the crew of the plane to disembark,” Interior Minister Chaudhry Nisar Ali Khan said in a statement.
He added: “Any deportee with the unverified documents will be sent back on the same flight to the country he would arrive (from). A European country has violated the Pakistani laws even after all matters were settled down with the commissioner of the European Union, it will not be allowed.”
Pakistan, the sixth most populous country in the world, is one of the top five countries of origin for illegal migration to Europe, according to figures from the European statistical institute Eurostat.