'Increased costs'

K+S said that the costs reflected "increased material and labour costs", besides some work on the group's historic infrastructure.

Even so "taking all data of the profitability calculation into account the project is economically attractive", Norbert Steiner, the K+S chief executive, said.

The scheme "still fulfils the requirement of the group, to earn a 15% premium on the cost of capital before taxes", he said.

Financing would be achieved in part through new debt.