Citing press articles on the furore, she said “there are doubts” as to whether “EEAS/Eulex Kosovo has properly investigated/is properly investigating the allegations of serious irregularities reported by the … Eulex prosecutor”.

The prosecutor - a seconded British official, Maria Bamieh - complained to her superiors that her colleagues took bribes to shut down criminal cases and stymied an internal affairs probe.

She was later fired on suspicion that she leaked documents to a Kosovo daily, Koha Ditore. But both she and the paper deny she leaked the files.

O’Reilly’s letter notes that EEAS/Eulex “have stated that a joint investigation was launched in 2013”.

It also notes the EEAS recently appointed a French academic, Jean Paul Jacque, to “assess the matter”.

The EU last week asked the UN to partly lift the immunity of one of the Eulex suspects, Italian judge Francesco Florit.

But with Bamieh claiming the 2013 internal investigation is “a lie … a complete joke”, O’Reilly complained that: “EEAS/Eulex Kosovo appear to have repeatedly declined to provide any information on what exactly the scope of this investigation was or what stage it has reached”.

O’Reilly added that Jacque’s mandate - to “check whether Eulex has adequate procedures to prevent corruption and whether it followed due process” - is so limited that she wants to make her own assessment “notwithstanding” his efforts.

She underlined that she will not look into Bamieh’s allegations as such, but will “verify whether EEAS/Eulex have taken all the necessary steps to examine” them.

She also asked Child to forward her “all the documents” related to the affair, promising to protect files which he “identifies as confidential” from “third parties”.

The EU Ombudsman, a Strasbourg and Brussels-based body, has around 90 staff and oversees “maladministration” in EU institutions.

Its reports are non-binding, but EU bodies have a track record of following up on its recommendations.

O’Reilly herself is an award-winning Irish journalist, who was also Ireland’s Ombudsman from 2003 to 2013.

Olaf involved

The Kosovo daily, Koha Ditore, reports that Bamieh, in her efforts to ring alarm bells inside the EU prior to her suspension, sent O’Reilly 40 pages of information in September.

It also reports that Bamieh sent the same dossier to the EU’s anti-fraud office, Olaf.

The Olaf press office told EUobserver it “does not usually confirm having received specific information regarding certain matters”.

Its protocol says Olaf specialists first evaluate “information of potential investigative interest” before deciding whether or not to open a case.

For their part, MEPs on the European Parliament’s foreign affairs committee have also voiced concern on Eulex in two behind-closed-doors meetings with top EEAS officials, including its new chief Federica Mogherini.

Meanwhile, Pieter Feith - the former head of the International Civilian Office in Pristina, which supervised Kosovo until 2012 - told this website that Mogherini should launch another, much wider investigation.

“It should look at the overall efficiency and impact of the rule of law mission” he said, noting that Eulex failed to convict a single high-level suspect in five years of work.

The more scrutiny the better

Commenting on the multiplication of probes, Richard Howitt, a British centre-left MEP, told EUobserver on Wednesday: “The seriousness of the allegations and what is, to me, the clear inadequacy of the investigations so far, justify as much external scrutiny as possible”.

“I therefore welcome the Ombudswoman’s efforts and I believe the parliament has a continuing role to play in addressing these issues”.

Eulex was in 2008 tasked with helping to create law and order in Kosovo.

It is the EU’s largest foreign mission, with more than 1,600 staff and a budget of €111 million a year.