The Abu Dhabi sovereign wealth fund is vowing to fight for its "legal rights" after filing a claim against Citigroup over its $7.5 billion investment in the bank.

A spokesman for the Abu Dhabi Investment Authority said Wednesday that it is ADIA's policy to pursue its "legal rights fully."

The fund declined to comment further, citing "binding confidentiality obligations." It also declined to provide a copy of the complaint.

Citigroup said late Tuesday that ADIA was seeking to terminate a deal made in 2007 to buy $7.5 billion worth of the bank's stock, or receive damages of more than $4 billion.