LONDON (Reuters) - The U.S. military has conducted an aerial survey of Greenland to assess the vast arctic island’s mineral potential as part of an agreement between the two governments, a top U.S. diplomat said on Wednesday.

The memorandum of understanding for cooperating on developing the mineral sector there was inked in June before a diplomatic flap between the United States and Denmark, to which Greenland is linked as an autonomous territory.

U.S. President Donald Trump called off a visit to Denmark scheduled for early September after the country’s prime minister rebuffed his idea of purchasing Greenland.

Frank Fannon, the U.S. assistant secretary of state for energy resources, told reporters at a gathering at London’s Chatham House that the process was “quite costly and technology intensive” and so Greenland had sought U.S. assistance.

“We had the navy there to shoot a hyperspectral survey, to basically use overflight technology to better understand the resource endowment.”

“That creates data room where the U.S. Geological Survey would be brought in to help interpret the data and share with the Greenlanders what the potential resource endowment might be.”

According to a press release by Greenland’s government, the aerial mapping would be jointly funded and involves surveying around 3,000 square kilometers in the territory’s southwestern Gardar province.

The data gathered would measure the reflection of sunlight, including infrared light invisible to the naked eye, to better understand the geology of the terrain and its mineral content.

Fannon added that the United States planned to help Greenland, armed with the data, to develop a regulatory structure to exploit mineral finds and market future tenders.

Asked if relations with Greenland or Denmark had deteriorated since Trump’s offer to buy the territory, Fannon responded: “I’ve only seen the strongest relationship with Greenland as well as with Denmark ... It’s a very positive relationship.”

Greenland is gaining attention as global superpowers including China, Russia and the United States look toward the Arctic region for mineral resources and strategic waterways.

A defense treaty between NATO allies Denmark and the United States dating back to 1951 gives the U.S. military rights over the Thule Air Base in northern Greenland.

After Trump canceled his planned meeting with his Danish counterpart in August, Greenland’s foreign minister Ane Lone Bagger told Reuters: “We are open for business, but we’re not for sale.”