The EU commissioner for home affairs will meet Greek and Croatian ministers on Thursday to discuss the latest media reports on migrant pushback.
"Some of these reports are shocking and I'm extremely concerned," Ylva Johansson told reporters about a joint investigation by media outlets Der Spiegel, ARD, and Liberation.
The reports presented evidence that Greek, Croatian and Romanian authorities had been violently pushing back asylum seekers crossing the bloc's external borders.
"There seems to be in the case, some kind of orchestration of violence at our external borders and there seems to be convincing evidence of misuse of (EU) funds," she said, implying the fact that the national authorities had received significant EU financial support for external border management.
Johansson promised that she would "raise the reports directly" when meeting Greek Minister for Migration, Notis Mitarachi, and Croatian Minister for Interior Affairs, Davor Bozinovic, later on Thursday.
Johansson stressed that these allegations had to be investigated.
"The (European) Commission strongly opposes any pushback practices and has repeatedly emphasized that any such practices are illegal," Adalbert Jahnz, the spokesperson on home affairs and citizenship said earlier on Thursday at the European Commission's daily press briefing.
He called the reports "very concerning mistreatment of migrants, asylum seekers and refugees that are unacceptable" and noted that the allegations "must be investigated", particularly in terms of respect for fundamental rights.
Jahnz also explained that the EU executive body "continues to have serious concerns, based on evidence and reports presented by both the European Parliament and UNHCR."
He noted that it is beyond the European Commission's competencies to investigate the acts of national authorities, but reassured that the institution had been helping member states in addressing "reports of unlawful activities and use extended borders."