South Korea has banned all fish imports from a large area of Japan in response to growing concern over the possible environmental impact of recent leaks of highly toxic water at the Fukushima Daiichi nuclear power plant.

In Japan, the row over the plant operator's handling of the leaks deepened on Friday when the head of the country's nuclear watchdog issued a stern rebuke to Tokyo Electric Power (Tepco) for causing unnecessary alarm overseas by releasing "scientifically unacceptable" information about radiation levels.

Seoul's decision came as Japan's prime minister, Shinzo Abe, prepared to make a final pitch for Tokyo's bid to host the 2020 Olympics.

Tokyo is the bookmakers' favourite but international concern over contamination at Fukushima Daiichi is fuelling speculation that the Japanese capital could lose out to Madrid or Istanbul. The International Olympic Committee will name the host city at a meeting in Buenos Aires on Saturday evening.

South Korea said it had imposed a total ban on fish from Fukushima and seven other prefectures in response to growing public fears over the safety of produce from the region. The fisheries vice-minister, Son Jae-hak, told reporters that the ban would stay in place indefinitely, adding that Japanese authorities had failed to provide timely and detailed information about the water leaks.

South Korea imported 5,000 tonnes of fish from the affected region last year, including stocks from Aomori in the far north, to Chiba, located east of Tokyo.

Despite assurances by Japan that it rigorously tests food for radiation, China has also maintained a ban on dairy, vegetable and seafood imports from several prefectures, including Fukushima, since March 2011.

"We have provided the South Korean government with relevant information since the contaminated water leaks," the chief cabinet secretary, Yoshihide Suga, said . "We will continue to ask South Korea to take measures based on scientific facts."

In a statement carried by the Yonhap news agency, South Korea's fisheries ministry said the ban had been necessary "as the government concluded that it is unclear how the incident in Japan will progress in the future and that the information the Japanese government has provided so far is not enough to predict future developments".

The impact from the recent water leaks was being felt as far away as Buenos Aires, where Japanese officials were besieged by questions about Fukushima ahead of the IOC's decisive vote.

Hiroshi Hase, an MP and former Olympic wrestler, told reporters in the Argentinian capital that contamination from Fukushima was "not even an issue" for the health of people in Tokyo, located 150 miles south of Fukushima Daiichi.

A Tepco employee in protective clothing works around water tanks at the Fukushima nuclear power plant in June. Photograph: Noboru Hashimoto/EPA

With the IOC decision imminent, Shunichi Tanaka, chairman of Japan's nuclear regulation authority, criticised Tepco for inflating fears around the world by releasing misleading data about the water leaks.

Earlier this week, the utility said it had detected measured radiation of 2,200 millisieverts an hour at a hotspot near a water tank. Tanaka said the measurement was misleading, and had prompted alarmist reports in the domestic and international media.

"What Tepco is talking about is the level of contamination," he said, "So to describe it with the unit 'millisieverts per hour' is scientifically unacceptable. It's like describing how much something weighs by using centimetres."

He said Tepco should have used the unit becquerel, which signifies the radioactivity levels in the water itself rather than the potential human exposure levels. "I have come to think they need to be spoon fed," Tanaka said of Tepco. "It is regrettable that Tepco has caused confusion and fear in the international community by spreading misleading information."

The 2,200-millisievert an hour reading, confirmed by Tepco, is accurate, however. The firm has been at pains to point out that most of the radiation was emitted as beta rays – as opposed to far more dangerous gamma rays – which travel only short distances and are easily blocked by protective clothing.

Concern has been voiced over the danger posed to the health of nuclear workers. Until recently, only two workers were responsible for checking the water tanks, and devices used to measure radiation have had to be replaced because they could not detect radiation levels of more than 100 millisieverts an hour. The number of workers checking the tanks has since been increased to almost 100, Tepco said.

Tanaka said reports that the water leaks represented another catastrophe at the plant had been overblown, adding that the quantity of radiation leaking into the Pacific Ocean would have "no meaningful effect" on the environment.

Officials from the Tokyo 2020 Olympic bid in Buenos Aires. Japan has been accused of providing misleading information over radiation levels so as not to disrupt the city's candidacy. Photograph: Alexander Hassenstein/Getty Images

Criticism of Tepco's failure to to deal with the buildup of huge quantities of radioactive water at Fukushima Daiichi has intensified since its belated admission last month that the plant was leaching 300 tonnes of contaminated water into the ocean every day. The cleanup operation has been further blighted by leaks from water storage tanks and high levels of radiation.

About 1,000 tanks containing a total of 335,000 tonnes of water have been built behind the plant, but efforts to remove dangerous radioactive substances from the water have been held up by technical glitches.

Earlier this week, Tanaka offered assurances that the stored water would not be discharged into the sea unless radiation levels had been brought down to legally acceptable levels. Coolant water that is being pumped into the wrecked reactors becomes contaminated when it comes into contact with melted uranium fuel. It then mixes with groundwater flowing in from the hills behind the plant, requiring workers to pump out and store an estimated 400 tonnes of the toxic liquid every day.

This week, the Japanese government announced almost 50bn yen (£320m) in emergency funds to build a frozen underground barrier to prevent groundwater from leaking into the reactor basements, and to develop a reliable water treatment system.