BERLIN (Reuters) - Lufthansa <LHAG.DE> said it was cancelling 830 short- and medium-haul flights on Friday, just over a quarter of its schedule, due to a strike by pilots, it said on Thursday.

Pilots represented by union Vereinigung Cockpit began the walkout on Wednesday, prompting the cancellation of almost 1,800 flights in the first two days of the strike action.

Friday's cancellations are for short- and medium-haul flights and will affect more than 100.000 passengers, the German airline said. Most long-haul flights will be unaffected, it added.

Lufthansa board member Harry Hohmeister said demands for a 20 percent pay hike were unsustainable for the airline's future.

(Reporting by Caroline Copley; Editing by Ludwig Burger)