FRANKFURT (AFP) - Lufthansa pilots late Monday announced their fifth strike since the end of August, this time grounding freight flights in Germany over a dispute surrounding retirement benefits.

Pilots of Lufthansa Cargo will stage a walkout from 1am GMT on Wednesday to 8.30am GMT on Thursday and will "not operate any flight departing from German airports", their union Cockpit said in a statement.

Cockpit says the German airline's management has been "stubbornly maintaining" its retirement reform plans, leaving the union with no choice but to launch new strikes.

Managers, however, said that they have "shown readiness to reach a compromise in discussions with Cockpit and had proposed new negotiations on the disputed questions". "In these conditions, this new call for work stoppage is neither comprehensible nor reasonable," the management said in a statement.

Other recent strikes carried out by the union have affected passenger flights, with the latest on Sept 30 hitting 20,000 travellers.

Lufthansa pilots can currently take paid early retirement from the age of 55. They are fighting a plan by the airline to raise the minimum age and to involve pilots in the financing of their pensions.