EU border agency Frontex on Wednesday said member states have provided less than a third of the personnel it requested to deal with the record influx of migrants.
Frontex, which coordinates border patrols and collects intelligence about the bloc's frontiers, had called on European countries Friday to provide 1,500 police and 50 readmission experts "to support Greece in returning migrants to Turkey."
Only 396 police officers and 47 readmission experts have been offered, according to a statement released Wednesday by the Warsaw-based agency.
"I am grateful to the countries who have offered (personnel)... but I urge other member states to pledge many more police officers if we want to be ready to support readmission to Turkey as agreed by the EU Council," Frontex head Fabrice Leggeri said.
Leggeri had earlier said: "It is important to stress that Frontex can only return people once the Greek authorities have thoroughly analyzed each individual case and issued a final return decision."
The European Union struck a landmark deal with Turkey last week to stem the massive influx of migrants.
The European Commission has said the implementation of the deal will require the mobilization of some 4,000 personnel, including a thousand security staff and military officers, and some 1,500 Greek and European police.
Frontex spokeswoman Ewa Moncure told AFP the officers requested by the agency were part of this figure.