By Abhijith Ganapavaram

NEW DELHI (Reuters) -India's largest airline IndiGo has entered an agreement with Air France-KLM, Virgin Atlantic and Delta to expand its long-haul services to North America, Europe and Britain, the airlines said on Sunday.

IndiGo has an extensive domestic network in India, the world's third-largest air passenger market, and is expanding its international reach.

Separately IndiGo also said it would convert 30 out of 70 options for Airbus A350 jets into firm orders for new planes.

Once the airline partnership is complete, IndiGo will be able to sell flights under its own name on those operated by its partners out of India, and onward travel from Amsterdam and Manchester, UK, on selected flights to Europe and North America.

IndiGo will start flying to Amsterdam and Manchester from July.

Air France-KLM and Virgin Atlantic already code-share on IndiGo's domestic flights. The Delta partnership is new.

U.S. carrier Delta has not flown to India since the pandemic. CEO Ed Bastian told media at an airline summit in New Delhi that Delta will restart direct services from the United States to India over the next couple of years.

"There's not a more important market in aviation at the present time than in India," Bastian said.

Delta is planning nonstop flights between Atlanta and Delhi, subject to government approval, a joint statement said.

IndiGo is hosting the International Air Transport Association's (IATA) annual meeting in New Delhi from Sunday.

IndiGo is aiming to grow its fleet to 600 aircraft by 2030, from more than 400 currently, and has been leasing aircraft to tide it over aircraft delivery delays and expand internationally.

It recently said it will lease six Boeing 787 wide-body jets from Norse Atlantic Airways by early next year.

India's aviation regulator said last week it would only extend an existing leasing arrangement IndiGo has with Turkish Airlines to the end of August.

The arrangement has been publicly criticised in India after Turkey came out in support of Pakistan during the recent conflict between the two South Asian neighbours.

(Reporting by Abhijith G and Rajesh Kumar Singh in New Delhi; Writing by Lisa Barrington in Seoul; Editing by Kirsten Donovan and David Holmes)