The head of the world's biggest sovereign wealth fund was forced out because his wife is Chinese

• Norwegian deputy central bank governor Jon Nicolaisen resigned on Friday after Norway's security service rejected his security clearance.
• Clearance was denied because Nicolaisen's wife is Chinese and resides in China. The pair have been married for ten years.
• As deputy governor Nicolaisen was in charge of the country's $1.2 trillion sovereign wealth fund, the biggest in the world.
• Norway has become stricter on ties to China and Russia in recent years, as its intelligence service says they are trying to find out information about the country's petroleum industry.

Norwegian deputy central bank governor Jon Nicolaisen announced that he was resigning on Friday, saying his application for renewed security clearance had been rejected because he has a Chinese wife.

In addition to setting monetary policy, Nicolaisen had been in charge of overseeing Norway's $1.2 trillion sovereign wealth fund, the world's largest.

"The Norwegian Civil Security Clearance Authority informs me that the reason that I will not receive a renewed security clearance is that my wife is a Chinese citizen and resides in China, where I support her financially," Nicolaisen said.

"At the same time, they have determined that there are no circumstances regarding me personally that give rise to doubt about my suitability for obtaining a security clearance, but that this does not carry sufficient weight."

"I have now had to take the consequences of this," he said.

Nicolaisen's resignation takes effect immediately, according to a statement released by the central bank. It was not immediately clear who would replace him.

Nicolaisen was not immediately available for further comment.

NATO-member Norway has become stricter in recent years regarding security clearances, making it difficult in many cases to get approval for anyone married to a person from a country with which Norway does not have security cooperation.

Nicolaisen was first appointed deputy governor in 2014 and was re-appointed to a second term in April of this year. The central bank said he and his wife had married in 2010.

The Chinese Embassy in Oslo was not aware of the resignation and its reasons, a spokeswoman told Reuters.

"I will miss Jon Nicolaisen in his post as deputy governor, where he performed his duties superbly as a close colleague and competent professional," Central Bank Governor Oeystein Olsen said in a statement.

Norway's PST intelligence service said that Russia, China, and other countries were using espionage to glean secrets of Norway's petroleum industry and its government's plans to cut or increase oil and gas production.

Norway is western Europe's largest petroleum producer with daily oil and gas output of around 4 million oil-equivalent barrels.