In December, the German airline's insolvency administrator sued Etihad for damages of up to 2 billion euros ($2.26 billion) in a Berlin court, saying Etihad did not meet its financial obligations towards Air Berlin.

State-owned Etihad filed its case on Wednesday in the High Court in London, a spokesman said.

(Reporting by Stanley Carvalho; editing by Saeed Azhar and Jason Neely)