A European regulator has found "issues" with Germany's aviation authority in a regular review of air safety enforcement, the European Commission said.
Its statement did not say when the review was carried out. But the Wall Street Journal said the Commission told Berlin in November "to remedy the long-standing problems" - months before last week's Germanwings crash that killed all 150 people aboard.
Separately, the aviation authority, the Luftfahrtbundesamt (LBA), told Reuters on Sunday that it did not know about co-pilot Andreas Lubitz's medical background prior to the crash.
Parent company Lufthansa has said Lubitz told officials at an airline training school he had gone through a period of severe depression in the past, raising questions over whether medical checks of crew members by the safety regulators and airlines are rigorous enough.
EU officials found that the LBA had a lack of staff, which could have limited its ability to carry out checks on planes and crew, such as medical checks, the Journal reported, citing two people familiar with the matter.
It said it was unclear whether the deficiencies identified at LBA were factors in the crash, however.
Vetting of airline crew is in the spotlight after the budget airline flight crashed in the French Alps. French prosecutors say they believe Lubitz crashed the plane deliberately.
"On the basis of EASA (European Aviation Safety Agency) recommendations, the Commission has addressed the issues to Germany to require compliance. Germany's replies are currently being assessed," the Commission spokesman said in the statement, emailed out on Saturday.
"All EU member states have findings and this is a normal and regular occurrence. It is part of a continuous system of oversight: findings are followed by corrective action, similar to an audit process," the Commission spokesman said, without specifying EASA's findings in Germany.
The spokesman was not immediately available for further comment.
A spokeswoman for the LBA said EASA's audits of national aviation authorities such as the LBA took place several times a year. She said the LBA had answered a single-figure number of criticisms levelled at it during the audits and those responses were now being assessed by EASA.
Lubitz
Asked whether Lufthansa's medical centres had informed the regulators about Lubitz's condition, Lufthansa said on Sunday it would not comment given the ongoing investigations.
German state prosecutors have said a computer found in Lubitz's home revealed searches on how to commit suicide as well as on cockpit doors and safety precautions related to them.
On Sunday German newspaper Bild am Sonntag said, without naming its sources, that investigators had found Lubitz used the username "Skydevil" to log on to the computer and had recently done internet searches on "bipolarity", "manic depression" as well as on "migraines", "impaired vision" and "acoustic trauma".
Bild had previously said that documents available to investigators had revealed Lubitz said he was in a car crash at the end of 2014 and had complained of resulting trauma and vision problems.
The public prosecutors' office in Duesseldorf was not immediately available for comment when contacted by Reuters.
French air accident authority BEA has said its investigation into the Germanwings crash would study "systemic weaknesses" that might have led to the disaster, including psychological profiling.
