Image copyright AP Image caption Japan insisted at the end of September that it was not engaged in spying in China

A Japanese woman is being detained by the Chinese authorities on suspicion of spying, Japanese media has reported.

The unnamed woman from Tokyo, said to be in her 50s, worked at a language school in the Japanese capital. She was detained while in Shanghai in June.

She is the fourth Japanese citizen to be detained on spying charges since May, all in different parts of China.

The move is likely to increase tensions between the two countries, the BBC's Jill McGivering says.

China has not commented on the latest report.

Image copyright Getty Images Image caption President Xi Jinping has toughened China's stance towards both internal dissent and foreign espionage

But our correspondent says the leadership in Beijing has toughened its stance on national security - with a new commission and stronger laws.

Sino-Japanese relations are already strained by revived war memories and tensions over the South China Sea.

The Japan Times reported that the woman who is being held had made several recent visits to China. The purpose of her most recent visit to China was unclear, it said.

China's foreign ministry confirmed at the end of September that two Japanese men were arrested in China on accusations of spying.

Japanese media reports said the men had been held since May, one in northern Liaoning province, the other in coastal Zhejiang province.

Japan's top government spokesman denied at the time that Tokyo spies on foreign countries, insisting that his country was "not engaged in such activity".

Reports of the Japanese detentions come not long after news emerged that an American woman, Sandy Phan-Gillis, had been held in China since March, also accused of spying.

In 2010, four Japanese men were detained in the northern province of Hebei for filming in a military area, during preparations for a bid by Japanese company Fujita to dispose of chemical weapons left in China by Japanese troops in the 1930s.

They admitted the filming but denied they knew they were in a restricted area, and were later released.