BERLIN, March 13 (Reuters) - Ground staff at Berlin's two airports will extend their strike until Wednesday morning, trade union Verdi said on Monday, stepping up action in a pay dispute that has already caused the cancellation of more than 1,000 flights since Friday.
The strike at Tegel and Schoenefeld airports - which is served by airlines including Air Berlin, Ryanair and Lufthansa - will now end on Wednesday at 0500 CET (0400 GMT).
Strikes at Berlin's two airports caused 660 flights to be cancelled on Monday as part of an ongoing pay dispute with ground staff. Lufthansa said it had cancelled 180 flights.
Ground staff are ready to engage in talks to end the strike if Berlin airports make an improved offer, Verdi said.
The union wants an increase in pay for ground staff to 12 euros ($12.80) an hour from about 11 euros as part of a one-year collective agreement. Management first offered about 10 cents more an hour over four years and then improved that offer to an 8 percent increase over three years. (Reporting by Boris Berner; Writing by Edward Taylor; Editing by Georgina Prodhan)