Lufthansa's pilots walked out on another strike today, forcing the carrier to cancel a further 890 flights, said a report.

The ongoing labour dispute, which has left thousand's of passengers stranded, has cost the carrier millions of euros and it will continue to lose more if negotiations are not made, said a report in the Daily Express.

Strikes by the carrier's pilots, which entered their sixth day this year, are costing Lufthansa about €15 million ($15.9 million) a day, a spokesman said today.

According to the report, the Union Vereinigung Cockpit (VC) wants an average annual pay rise of 3.7 per cent for 5,400 pilots over a five-year period backdated to 2012.

Lufthansa has so far offered to increase pilots' pay by 4.4 percent in two instalments and make a one-off payment worth 1.8 months' pay.

The strike is the 15th since early 2014, and the costs are mounting.

Walkouts in 2015 by both pilots and cabin crew affected 7,748 flights, costing Lufthansa €231 million ($245 million) in lost profit, with around €108 million ($114.5 million) of that coming from lost advance bookings.

Including last week's four-day walkout, Lufthansa has cancelled 4,500 flights so far this year due to strikes, and analysts have said the carrier's 2016 profit target could be at risk.