Fears grow as more suspicious drones appear above Norway's offshore facilities

News of unidentified drones buzzing in the skies above the North Sea in recent days has made Oslo increasingly concerned that the Kremlin might target its offshore facilities in a bid to intimidate its competition.

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

Prime Minister Jonas Gahr Støre has invited the navies of NATO allies -- France, Germany, and the UK -- 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," Ståle 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 kilometres of gas pipelines that spider from Norway's sea platforms to terminals in the UK and mainland Europe.

Since the start of the war in Ukraine in late February, European Union countries have scrambled to replace their