Abu Dhabi Investment Authority (ADIA), the UAE's largest sovereign wealth fund, will invest about $750 million in the debt of India's GMR Group, giving it a foothold in one of the world's fastest-growing aviation markets.

The investment will also allow the Indian company to reduce the pledged shareholding on its airports business.

ADIA has invested in structured debt instruments of a unit of GMR Enterprises (GEPL), the holding company of GMR Group. GMR Enterprises owns a roughly 25% stake in GMR AirportsGMRI.NS.

The funds will be used to refinance all external debt of GMR Enterprises, which is looking to lower its pledge on the shareholding of GMR Airports "significantly", GMR Group said in an exchange filing.

GMR Enterprises' total debt had increased nearly 4% year-on-year to 44.77 billion rupees ($532.5 million), according to its latest annual report.

"This investment from ADIA will facilitate the repayment of all external debt at GEPL, strengthening our ability to support the continued growth of GMR Airports," said GMR Group Corporate Chairman Kiran Grandhi.

India's domestic passenger traffic is expected to double to 300 million by 2030.

($1 = 84.0700 Indian rupees)

(Reporting by Yagnoseni Das and Meenakshi Maidas in Bengaluru; additional reporting by Hritam Mukherjee, Nandan Mandayam; Editing by Sonia Cheema)