Vietnam's government said toxic discharges from a Taiwanese-owned steel plant were responsible for massive fish deaths that have decimated tourism and fishing in four provinces and highlighted the risks of rapid growth in foreign investment.

An estimated 70 tons of dead fish washed ashore along more than 200 kilometers (125 miles) of Vietnam's central coastline in early April, sparking rare protests across the country when authorities could not initially pinpoint the cause.

A government minister, Mai Tien Dung, told reporters on Thursday that Formosa Ha Tinh Steel Corp., a subsidiary of Taiwan's Formosa Plastics Group, admitted it had caused the environmental disaster and has pledged $500 million to clean up the environment and compensate affected people, including helping fisherman to find new jobs.

Dung said waste water containing toxins such as cyanide and carbolic acids was released into the sea during a test run of the plant.

Formosa's $10.6 billion steel complex, which includes a steel plant, a power plant and a deep sea port, is one of the largest foreign investments in Vietnam. The country's authoritarian government, hoping to boost economic growth and reduce poverty, has overseen an influx of foreign investment deals amounting to least $70 billion in the past decade. But ordinary Vietnamese have become increasingly aware of and concerned by the environmental and human costs of such rapid development.

A Vietnamese fishing industry group said it was a positive that the government was holding Formosa to account, but said much more needs to be done to restore the health of the environment in the four affected provinces Ha Tinh, Quang Binh, Quang Tri and Thua Thien Hue.

"There are no fish or shrimp for fishermen to catch, seafood farming is impossible and the tourism industry has also been affected," said Nguyen Tu Cuong of the Vietnam Fishery Association. He said most fishermen can't easily switch to another occupation as the only skill they know is fishing.

Phan Thanh An, a fisherman from Quang Tri province, said that for 15 days after the dead fish began washing ashore, "I did not catch any live fish, only fish bones."

"I have never seen such massive amounts of dead fish like that before," he said.

An, who has been fishing since he was 13, said he hasn't taken his fishing boat out for two months but may try next week.

The chairman of Formosa Ha Tinh Steel, Chen Yuan-Cheng, apologized in a video shown at the news conference on Thursday.

"Our company takes full responsibility and sincerely apologizes to the Vietnamese people ... for causing the environmental disaster which seriously affected the livelihood, production and jobs of the people and the sea environment," he said.

The parent company, Formosa Plastics Group, is one of the world's biggest producers of poly vinyl chloride and has a patchy environmental record. Its U.S. subsidiaries agreed to pay millions of dollars in fines and remediation costs in 2009 after a long-running battle over air, water, and hazardous waste violations at two petrochemical plants in Texas and Louisiana.

Chen said the company was working to fix shortcomings at the steel plant's waste water treatment facility that were behind the disaster.

Separately, state media reported that the Vietnam Environment Administration had ordered inspections of a Chinese paper factory in the Mekong Delta province of Hau Giang because of concerns its waste water treatment system was discharging toxins that could pollute the Mekong River and kill fish.

Deputy Minister of Planning and Investment Dang Huy Dong said that the government wants to attract foreign investment that is technologically advanced and friendly to the environment, and will not lure investment at any price.

"We will not trade the environment for foreign direct investment," he said.