ATHENS, Greece (AP) — Greece’s energy and environment minister says U.S. energy giant ExxonMobil has begun prospecting for natural gas off the coast of southwestern Greece, kicking off a delayed project as Europe seeks alternative energy sources due to the war in Ukraine.

ExxonMobil’s ship is already in operation in the area, Energy and Environment Minister Kostas Skrekas said on state-run ERT television Thursday, just four days after Greece’s prime minister announced the project was to start. The move comes amid heightened tensions with neighboring Turkey, and is a project that has been heavily criticized by environmental groups.

“The ship has begun. At this moment it is laying the cables” which are needed for the sonic waves used in the prospecting, Skrekas said.

“The reserves we speculate exist southwest of Crete and the Peloponnese might be the last hope the mining industry has to find a large reserve … in the region of southeastern Europe, in our region,” he said. However, he noted, “until we drill and see what is really there, everything is on the level of speculation.”

If the seismic testing does indicate the existence of reserves, exploratory drilling could begin in 2025, Skrekas said.

Environmental groups have argued that deep-sea prospecting for resources would have “unbearable” consequences on vulnerable populations of whales and dolphins. Critics also highlight the potential risk of spills, and say the project, if successful, would increase Greece’s use of fossil fuels amid the planet’s climate change crisis.

Skrekas stressed that all measures are being taken to ensure the protection of the environment and of marine mammals living in the area.

“All research is being done with the basic priority of the protection of the environment,” he said, speaking later in the day at Greece’s Foreign Press Association. If viable gas deposits are eventually found, “no discounts will be made regarding safety and environmental protection” in any potential mining operations, he said.

Skrekas, who holds the portfolios of both energy and environmental affairs, insisted there would be no conflict of interest between the two, and that the main emphasis would be on environmental protection.

“It is not allowed for there to be a conflict between these two. The priority is the protection of the environment,” he said. “In no case will we make discounts in environmental protection in order to advance with human activity.”

The block reserved for the exploration includes part of the Hellenic Trench, where the Mediterranean’s deepest waters lie at more than 5,000 meters (17,000 feet). The area is a vital habitat for the sea’s endangered sperm whales, and for other cetaceans already threatened by fishing, collisions with ships and plastic pollution.

The mammals are particularly sensitive to the underwater noise produced by seismic surveys for fossil fuels, in which sound waves are bounced off the seabed to locate potential deposits. Sonar used by warships has been shown to have deadly effects on whales, and experts say seismic surveys can do the same.

Meanwhile, the prospecting also comes at a time of heightened tension with Turkey, with which Greece has been at loggerheads over offshore exploration rights in the eastern Mediterranean. Turkish prospecting east of the southern Greek island of Crete two years ago prompted a military buildup.

European countries have been scrambling to replace their former dependency on Russian fossil fuels following Russia’s invasion of Ukraine in February and the subsequent damaging of pipelines designed to carry natural gas from Russia to Germany.