Euro zone producer prices fell unexpectedly in April, registering the steepest annual decline in more than six years due to sharply lower energy costs, data from the European Union's statistics office Eurostat show. 

Eurostat said prices at factory gates in the euro zone dropped by 0.3% month-on-month for a 4.4% year-on-year decline. 

This was the greatest annual decline since November 2009. 

Analysts polled by Reuters had on average expected a 0.1% month-on-month rise and a 4.1% drop on a yearly basis. 

Excluding the 1.1% fall in energy, producer prices were up 0.1% in April, compared to a 0.1% decline in March. 

The positive reading was due to slightly higher prices for intermediate, capital and durable goods, with non-durable goods prices falling. 

Euro zone energy prices fell 1.1% after a 1.1% increase in March. On an annual basis, energy prices were 12.5% lower.

While the data relates to April, it shows the struggle the European Central Bank is facing in bringing consumer price inflation back to its target of below but close to 2% over a two-year horizon. 

The euro zone was in deflation for a second consecutive month in May.