Feb 26 (Reuters) - Franco-Italian automaker Stellantis said on Monday it had reached a multi-billion-euro frame agreement with leasing and fleet management company Ayvens to sell up to 500,000 vehicles across Europe over the next three years.

Under the agreement, Ayvens' affiliates will buy the vehicles for its long-term leasing fleet across Europe, with the first delivery volumes expected to begin in the first half of 2024, Stellantis said.

Stellantis, which owns brands including Chrysler, Jeep and Fiat, said specific details of the deal including order quantity, compositions and delivery dates beyond the volumes already planned for 2024 can be flexibly agreed between the two companies, depending on fleet requirements and demand.

Ayvens' customers will be offered brands such as Alfa Romeo, DS Automobiles, Fiat, Opel, Peugeot, and Vauxhall, the statement said, adding that the brand availability can be extended in the future to cover Stellantis' entire portfolio.

The agreement "will aid the progressive transition of Ayven's client base to choosing more sustainable mobility options," Stellantis Chief Executive Carlos Tavares said.

Ayvens was created when ALD Automotive, a subsidiary majority owned by French lender Societe Generale, acquired fleet management and mobility company LeasePlan last year. (Reporting by Angela Christy and Giulio Piovaccari; Editing by Sherry Jacob-Phillips)