FRANKFURT (Reuters) - German carrier Lufthansa <LHAG.DE> and pilots' union Vereinigung Cockpit (VC) have extended talks again over pay and retirement terms to try to resolve a long-running dispute that has led to more than a dozen strikes.

"Due to the high complexity and the scale, an agreement on all the issues could still not be reached, despite extended talks," the pilots' union said in a statement on Saturday, adding negotiations would resume at the beginning of next week.

The carrier is trying to cut costs at its main brand in Germany to help it to compete with low cost rivals in Europe and fast-growing long-haul carriers such as Emirates and Turkish Airlines.

The dispute with the pilots stretches back over four years, with the two sides needing to agree pay deals for contract periods from May 2012, plus reach agreement over changes to a decades-old scheme that allows pilots to retire early from the age of 55 and keep a proportion of their pay.

The pilots' union also said that "significant progress" had been made during a non-stop 24-hour round of talks that ended early Saturday, but gave no further details.

Lufthansa and the union had previously aimed to reach agreement before the end of July, before talks were extended to Friday.

The group in July agreed a deal with its main cabin crew union on pay and conditions, which is now being voted on by union members.

Lufthansa CEO Carsten Spohr has said that even if the carrier failed to bring talks with the pilots' union to a successful conclusion, Lufthansa would still reduce costs because it would transfer jobs to collective labor contracts at its Eurowings budget subsidiary.

(Reporting by Christoph Steitz and Victoria Bryan. Editing by Jane Merriman)