Japan said on Monday that it had summoned China's ambassador over a spate of nuisance phone calls over Tokyo's plan to release treated nuclear wastewater into the Pacific.

 On Thursday, Japan started to release treated water from the defunct Fukushima nuclear power plant, which suffered meltdowns after it was hit by a tsunami in 2011. Japan's neighbors have been critical of the move.

Beijing has said that Tokyo had not proved the water would be safe and issued a ban on all aquatic products from Japan.

'Regrettable' phone calls over Fukushima plans

"A lot of harassment phone calls believed to be originating from China are occurring in Japan ... These developments are extremely regrettable and we are concerned," Chief Cabinet Secretary Hirokazu Matsuno told reporters.

Japan's Foreign Ministry said that Japanese facilities in China were also receiving such calls. It urged Beijing to ensure the safety of Japanese citizens.

Japan's prime minister also spoke of "regrettable" phone calls and other acts of harassment.

"There have been numerous harassment calls believed to originate from China and instances of stones being thrown into the Japanese embassy and Japanese schools. It must be said these are regrettable," Fumio Kishida told reporters.

"We summoned the Chinese ambassador to Japan today and strongly urged him to call on Chinese people to act in a calm and responsible manner," Kishida said.

What have Chinese officials said about the calls?

A spokesman for China's foreign ministry said it was not aware of the matter when asked about the accusations earlier on Monday.

"China always safeguards the safety and lawful rights and interests of foreign nationals in China in accordance with law," Chinese Foreign Ministry spokesperson Wang Wenbin said when asked about the phone calls and an incident where a rock was thrown at a Japanese school in the Chinese city of Qingdao.

Meanwhile, the Chinese embassy in Tokyo spoke of "a large number of nuisance calls from Japan."

Ambassador Wu Jianghao said that the calls have caused "serious interference in the normal operation of the embassy and consulates."

sdi/ab (AFP, Reuters)