A rush to drill in the gas-rich Mediterranean may do permanent damage to the sea's wildlife as it takes at least a millennium for an ecosystem to grow, the World Wildlife Fund warned Wednesday.

Drilling in the Mediterranean's eastern region shared by Turkey, Israel and Egypt, "could cause irreversible damage" to its biodiversity, said Sergi Tudela, head of WWF's Mediterranean Fisheries Programme.

The area hosts rare and millennia-old species such as deep-sea sponges, worms, mollusks and cold water corals, and therefore are "particularly fragile and vulnerable to external interference," he added in a statement.

Once a deep-sea floor has been drilled, "it can take a millennium or more before the unique micro-ecosystem grows again, so the most fragile and valuable species and under-sea areas must be left untouched by gas development."

The recently discovered Leviathan gas field, 135 kilometres off the Israeli coast, is the world's biggest deep-water gas discovery in a decade, with an estimated volume of 16 trillion cubic feet of gas.

Earlier this year the West Nile Delta gas field was discovered, lying in Egyptian waters 80 kilometres off Alexandria.

The green group called on a handful of Mediterranean countries and the European Union to ban industrial development and drilling in deep-sea areas where the biodiversity is rich.