A Chinese state-run newspaper Thursday urged Beijing to say whether its ambassador to Iceland was a spy following reports he had been held for leaking intelligence to Japan, while authorities said they had "no information" on the matter.

The editorial by the Global Times newspaper, which is run by the ruling Communist Party's mouthpiece the People's Daily, throws a rare official spotlight on such cases.

Envoy Ma Jisheng left Iceland mysteriously in January and has not been replaced, with Beijing only telling Reykjavik that he was unable to return for "personal reasons", according to the Icelandic foreign ministry.

The embassy website contains a link titled "CV of Ambassador", but the resulting page is blank.

Ma's name has also been removed from the embassy's directory listing on the Chinese foreign ministry homepage.

Asked for an update on Ma's case Thursday, foreign ministry spokesman Hong Lei said: "I have no information in such regard".

In its editorial, the Global Times urged Beijing to clear the air, citing the need to raise public awareness of espionage risks.

Few spying cases involving Chinese officials have been reported in the domestic media, it said.

"In actuality, reporting such incidents will educate many people by letting them know how close those manipulators of overseas intelligence agencies are to us," the newspaper said.

Hong Kong's Ming Pao daily, citing US-based Chinese-language website Mingjing News, reported that Ma and his wife "were suspected of giving state secrets to Japan and were arrested (in early February) by the Ministry of State Security."

Ma was a high-ranking diplomat in Japan from 2004-08.

- 'A warning for others' -

The Global Times argued that those engaged in espionage were increasingly likely to be caught due to advances in investigation technology.

"All the potential high-risk groups should recognise this point, which may help them refrain from selling information when they are about to cross the red line," it said.

"If it is confirmed that Ma has been caught, we hope that his story will one day appear on media to serve as a warning for others," the paper added.

Ming Pao said the Ma case, if confirmed, would mark the second case of an ambassador-level Chinese official caught in an espionage scandal.

In December 2006, then-ambassador to South Korea Li Bin was investigated and detained on suspicion of providing intelligence to Seoul. He was later sentenced to seven years in prison on economic charges, it said.

Ma's disappearance comes as a US congressional panel is lobbing its own espionage accusations against Beijing.

According to a report released Wednesday by the US Senate Armed Services Committee, Beijing-linked hackers carried out at least 50 cyberattacks on US defence contractors between 2012 and 2013, potentially compromising military operations.

"Of those 50, at least 20 were successful intrusions into contractor networks attributed to an 'advanced persistent threat' (APT), a term used to distinguish sophisticated cyber threats that are frequently associated with foreign governments," the report warned.

Beijing on Thursday flatly rejected the accusations, which foreign ministry spokesman Hong called "fabricated out of thin air".

"Chinese law prohibits cyberattacks and other crimes, and cracks down on such crimes," Hong said. "The Chinese government and military will never support hacker attacks."