An EU border agency probe into allegations of illegal migrant pushbacks on the Greece-Turkey maritime border has proven inconclusive, according to a report seen Wednesday by AFP.

The report by a working group appointed by Frontex management, which was shared by a source close to the investigation, said it was "not able to clarify completely" the details of five incidents of alleged rights violations.

But the working group did point to "deficits and the need for improvement of the reporting and monitoring system" in place.

"The existing legal framework only offers limited options for Frontex for action in the event of reported and established legal violations," the report stated.

The investigation will be the main topic at an extraordinary meeting of the Warsaw-based agency’s board on Friday.

The working group also emphasized the "difficult circumstances of conducting border police measures at the EU external maritime border in the Aegean Sea faced by all stakeholders."

It concluded that action by Frontex chief Fabrice Leggeri to halt operations in the Aegean Sea "would not be justified."

Pushbacks prevent asylum-seekers from making refugee claims and if practiced indiscriminately against a group of migrants can constitute "refoulement," a violation of core EU human rights laws and the 1951 Geneva Convention.

Leggeri has been under pressure for weeks over the allegations as Frontex takes on a greater frontline role in patrolling EU borders.

MEPs and activists have called for him to resign over the operations, but he has refused to, insisting the agency is key to the fight against human trafficking.

Created in 2004, Frontex has become the first EU agency to build up a standing, uniformed force. It aims to have 10,000 border guards by 2027.

Meanwhile, the agency is also being investigated by OLAF, the independent EU corruption watchdog.

In early December, EU lawmakers lashed out at Frontex’s executive director over allegations that the agency helped illegally stop migrants entering Europe and supported Greek coast guards to push migrants back toward Turkish territorial waters in the Aegean Sea, calling for his resignation and demanding an independent inquiry.

The lawmakers grilled Executive Director Fabrice Leggeri over an investigation in October by several international media outlets, which said video and other publicly available data suggest Frontex "assets were actively involved in one pushback incident at the Greek-Turkish maritime border in the Aegean Sea."

While the border agency is required to rescue migrants, the Frontex vessels patrolling the area sped past the overcrowded, inflatable boats, creating dangerous waves to force them to return to Turkish shores. A Frontex aircraft was also documented passing over migrants, who were seeking help at sea, but did not rescue them.

Turkey and Greece have been key transit points for migrants aiming to cross into Europe, fleeing war and persecution to start new lives. Turkey has also accused Greece of large-scale pushbacks and summary deportations without access to asylum procedures, which is a violation of international law. It also accuses the EU of turning a blind eye to what it says is a blatant abuse of human rights.