German annual inflation slowed to its weakest rate in nearly four years in May as the cost of energy fell, preliminary data released by the Federal Statistics Office showed on Monday.

Consumer prices rose by 0.9 percent compared to the prior year period, the lowest level since June 2010. Economists polled by Reuters had expected consumer price inflation to slow to 1.1 percent in May from 1.3 percent the previous month.

On a monthly basis, consumer prices fell 0.1 percent compared with a drop of 0.2 percent in April.

Consumer prices harmonized to compare with other European Union countries showed a monthly drop of 0.3 percent and a year-on-year rise of 0.6 percent after a monthly decrease of 0.3 percent and an annual rise of 1.1 percent in April.

Final German price data for May are due to be released on June 13, the office said.