Fears over Russian threat to Norway’s energy infrastructure

Norwegian oil and gas workers normally don't see anything more threatening than North Sea waves crashing against the steel legs of their offshore platforms. But lately they have noticed a more troubling sight: unidentified drones buzzing in the skies overhead.

With Norway replacing Russia as Europe's main source of natural gas, military experts suspect the unmanned aircraft are Moscow's doings. They list espionage, sabotage and intimidation as possible motives for the drone flights.

The Norwegian government has sent warships, coastguard vessels and fighter jets to patrol around the offshore facilities.

Norway's national guard stationed soldiers around onshore refineries that also were buzzed by drones.

Prime Minister Jonas Gahr Store has invited the navies of NATO allies Britain, France and Germany to help address what could be more than a Norwegian problem.

Precious little of the offshore oil that provides vast income for Norway is used by the country's 5.4 million inhabitants.

Instead, it powers much of Europe. Natural gas is another commodity of continental significance.

"The value of Norwegian gas to Europe has never been higher," Stale Ulriksen, a researcher at the Royal Norwegian Naval Academy, said. "As a strategic target for sabotage, Norwegian gas pipelines are probably the highest value target in Europe."

Closures of airports, and evacuations of an oil refinery and a gas terminal last week due to drone sightings caused huge disruptions. But with winter approaching in Europe, there is worry the drones may portend a bigger threat to the 9,000 kilometers (5,600 miles) of gas pipelines that spider from Norway's sea platforms to terminals in Britain and mainland Europe.

Since the start of the...