In a joint sunrise operation involving divers and boats backed by helicopters and drones, drug enforcement agents and local police raided the Hevsel Gardens in Diyarbakir in the mainly-Kurdish southeast, IHA news agency and Cumhurriyet newspaper reported.

They did not say when the raids took place.

Inside the gardens, which cover an area stretching some 700 hectares (1,700 acres) between Diyarbakir Fortress and the Tigris River, they found thousands of marijuana plants growing at 31 locations.

The plants would have yielded about 5.3 tonnes of cannabis, worth approximately two billion Turkish lira ($51 million), the reports said.

There was no immediate comment from the interior ministry.

The growers had taken advantage of the fact that vehicles cannot enter Hevsel Gardens, due to the nature of the terrain, to set up tents to conceal and protect the plants, and were using irrigation systems to draw water from the Tigris, the reports said.

It was not immediately clear whether anyone had been arrested.

In 2015, the terraced gardens -- which are still used for growing agricultural crops -- were recognised as a UNESCO World Heritage site alongside Diyarbakir fortress, in an acknowledgement of their historical and cultural significance.

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