BERLIN (AP) — The insolvency administrator for bankrupt airline Air Berlin has sued its former largest shareholder, Gulf airline Etihad, for 2 billion euros ($2.26 billion) in damages, a Berlin court said Friday.

The suit alleges United Arab Emirates-based Etihad failed to live up to its financial obligations by withdrawing funding from the struggling airline, according to the Berlin administrative court.

In a statement, the court said Etihad had been supporting Air Berlin and sent a so-called "comfort letter" in April 2017 assuring its continued backing for 18 months. But it then stopped the funding in August 2017, forcing Air Berlin to file for bankruptcy.

ARCHIVES: Air Berlin files for bankruptcy after Etihad pulls plug

The suit asks for 500 million euros compensation and unspecified further damages, which the court estimated in total at some 2 billion euros.

Etihad, which has until the end of January to respond to the legal filing, confirmed that it had received the claim.

"We believe that the claim is without merit and will defend ourselves vigorously against it," the airline told The Associated Press in an email.

ARCHIVES: Germany's bankrupt Air Berlin will end flights this month (October 2017)

ARCHIVESGerman court rules against Etihad-Air Berlin codeshares

ARCHIVESGermany limits Air Berlin-Etihad codeshare flights

PHOTO ARCHIVES: Etihad Airways shows off new Airbus A380, Boeing 787 and crew uniforms

EPA GERMANY TRANSPORT AIRBERLIN INSOLVENCY EBF TRANSPORT DEU
An Air Berlin plane is seen at Berlin's Tegel Airport on Aug. 15, 2017.
EPA