Italian energy giant ENI on Sunday announced the discovery of the "largest ever" offshore natural gas field in the Mediterranean inside Egypt's territorial waters.

The discovery, confirmed by Egypt's oil ministry, could hold a potential 30 trillion cubic feet (850 billion cubic metres) of lean gas in an area of about 100 square kilometres (40 square miles), it said in a statement.

The so-called Zohr project is "the largest gas discovery ever made in Egypt and in the Mediterranean Sea," it said, adding the find would meet Egypt's own natural gas demands for decades.