ISTANBUL, April 29 (Reuters) - Turkish Airlines is negotiating with both Airbus and Boeing about buying 235 aircraft as part of its expansion plans, Chairman Ahmet Bolat said on Monday.

The airline's 10-year fleet plan, unveiled last year, shows it aims to expand by almost 600 planes. In December it announced a deal with Airbus for 355 firm and optional orders for A321 narrow body and A350 wide body aircraft.

"We are negotiating with both Airbus and Boeing for the remaining 235 planes," Bolat said at an event held with Airbus and Rolls-Royce in Istanbul.

Turkish Airlines "has always followed a balanced policy between Airbus and Boeing", he said, adding it was waiting for problems faced by Boeing to end, so was not in a hurry to reach a decision.

A January mid-air blowout of a cabin panel led Boeing to slow production of its best-selling jet.

Bolat also said Rolls-Royce was exploring potentially establishing maintenance, repair and overhaul capabilities in Turkey, as well as further supply-chain sourcing.

The event was held to unveil a strategic programme that Turkish Airlines created along with Airbus and aerospace companies in Turkey to develop the Turkish aerospace industry.