South Korean flag carrier Korean Air said Thursday it will sign a $13.7 billion deal with Airbus to purchase 33 A350 series aircraft to strengthen its long-term fleet operations.

The move comes after the European Union approved the airline's takeover of smaller rival Asiana -- conditional on the firm fulfilling commitments to allay competition concerns -- that would take its fleet to over 200 aircraft.

"The procurement of the next-generation, eco-friendly A350 is not only aligned with the airlines' sustainability efforts, but also is seen as preparation for the integration of Asiana Airlines," Korean Air said in a statement.

The deal involves the purchase of 27 A350-1000 and six A350-900 aircraft, Korean Air said.

The A350-1000s are the largest in the A350 fleet and can operate "up to 16,000km (9,942 miles) with full payload" of up to 410 passengers, the airline added.

"The aircraft makes use of advanced composite materials, resulting in reduction in fuel consumption and carbon emissions of up to 25 percent."

The smaller A350-900 variant can carry around 300-350 passengers in a three class configuration, the company said, deployable on long-haul routes with a range of 15,370 kilometres.

Korean Air has historically favoured aircraft from Airbus competitor Boeing, but the US manufacturer has been hit by a series of safety issues including a near-catastrophic incident in January when a fuselage panel on a Boeing 737 MAX 9 Alaska Airlines jet blew off mid-flight.

However, Korean Air said it had plans to introduce a further "50 Airbus A321neos, 10 Boeing 787-9s, 20 Boeing 787-10s, and 30 Boeing 737-8s" down the line.

The purchases are part of the airline's plans to "prioritize fleet modernization and reduction of carbon emissions" through newer aircraft.

The Asiana takeover is currently awaiting final approval from US antitrust authorities after gaining approval from 13 countries and regions.