China's foreign ministry has refused to address the whereabouts of its ambassador to Iceland after reports he has been detained for giving secrets to Japan.

Ma Jisheng left Reykjavik for China in January this year but did not return in March as expected. A New York-based Chinese language site reported on Tuesday that he and his wife had been seized by state security on suspicion of espionage.

Ma served in China's embassy in Tokyo twice, finishing his last posting in 2008. The allegations are particularly sensitive given the marked deterioration in relations between China and Japan in recent years, and especially since the election of prime minister Shinzō Abe.

The two countries are locked in a long-running territorial dispute over uninhabited islands in the East China Sea, known as the Diaoyu to the Chinese and Senkakus to the Japanese, and China complains Japan has failed to fully atone for its brutality in the second world war.

Ma's lengthy absence from Reykjavik was first highlighted by an Icelandic newspaper this month. He has been ambassador only since December 2012 – meaning that if he is not returning his posting has been cut unusually short.

Mingjing News then reported the espionage claims, with Hong Kong's Ming Pao newspaper picking up the story. Some mainland Chinese news sites carried the reports but subsequently deleted them.

Asked whether the reports were true, Hong Lei, spokesman for the Chinese foreign ministry, said: "I have no information on this." He gave the same answer when asked for Ma's current whereabouts and to clarify who was the Chinese ambassador to Iceland.

A spokeswoman for Iceland's foreign ministry, Urdur Gunnarsdóttir, confirmed that Ma was to have returned in March. She said the Chinese embassy in Reykjavik had stated in May that he would not return to his post for personal reasons. There has been a caretaker ambassador since then, Gunnarsdóttir said.

Ma's CV has been deleted from the website of the Chinese embassy in Iceland and it has a blank where his name would normally appear in a welcoming address. The last reference to him in the news section dates from September last year. Older articles about him were still visible there and on the foreign ministry website.

Ma was a secretary at the Chinese embassy in Japan between 1991 and 1995, and a minister counsellor between 2004 and 2008. Prior to becoming ambassador to Iceland, he worked as deputy director of information in the foreign ministry. A Japanese government official told Reuters: "We are aware of the media report. But it's basically China's domestic issue and therefore the Japanese government would like to refrain from commenting."

In 2012 there were reports that a Chinese state security official, working as an aide to a vice-minister, had been arrested on suspicion of spying for the US.

The best-known spying scandal involved Yu Qiangsheng, a senior intelligence official who defected to the US in 1985 and told the Americans that a retired CIA analyst had been spying for China. The man he named killed himself days before he was due to be sentenced by a US court.

Yu's brother Yu Zhengsheng prospered politically despite the family connection and is now a member of the Politburo Standing Committee. It has not been possible to contact Ma.