A deputy mayor who assured the public that an explosion at a petrochemical plant in northeastern China caused no pollution has been found dead in his home, officials said Wednesday.

The Chinese government, meanwhile, pledged for the first time to punish anyone who tried to cover up the massive toxic spill caused by the blast.

In a sign of the political sensitivity of the case, state media did not report the death of Wang Wei, deputy mayor of the city of Jilin, where the Nov. 13 accident occurred. But several city officials confirmed that he was discovered dead Tuesday, and a journalist familiar with the situation said he was believed to have committed suicide.

Because he was responsible for industrial safety in Jilin and played a prominent role in the city's response to the explosion, Wang, 43, was expected to be questioned and perhaps prosecuted, and he could have incriminated others involved in the 10-day effort to hide the toxic spill from the public.

The death heightened the sense of crisis that has surrounded the Communist Party's struggle to address the environmental disaster on the Songhua River and ease the public anger that the slow and secretive initial response to the spill has generated here and abroad.

The spill of 100 tons of benzene and other carcinogenic chemicals into the Songhua has caused disruptions in water supplies to millions in the region, including a five-day shutoff of water in the major city of Harbin. The long toxic slick is slowly diluting and moving toward Russia, where it is expected to arrive early next week at the border city of Khabarovsk.

Chinese officials are drafting plans at the request of the Russians to build a temporary dam at the mouth of a shallow channel to prevent pollutants from entering a source of the city's water supply on the Ussuri River, state media reported Wednesday. The Songhua flows into the Heilong River, part of which flows into the Ussuri through the channel.

The Chinese government has already apologized to Russia for the spill and offered equipment and technical assistance. Talks are also said to be underway concerning financial compensation for damages.

Meanwhile, China has accepted an offer from the Bush administration to help assess the long-term impact of the spill, a U.S. Embassy spokeswoman said.

In another setback to President Hu Jintao's efforts to prove that his government is serious about enforcing industrial safety rules and preventing further accidents, a gas explosion at a recently privatized coal mine in the eastern province of Hebei killed 74 miners Wednesday, with 32 others still missing early Thursday, state media said.

The blast was the fourth major accident in less than a month in China's coal mines, the world's deadliest with as many as 10,000 miners killed every year. Rescuers on Tuesday recovered the body of the last miner missing in the worst of the recent accidents, an explosion at a state-owned mine in northeastern Heilongjiang province on Nov. 27 that killed 171 miners.

The recent accidents have highlighted the government's inability -- some say unwillingness -- to enforce safety and environmental protection regulations. Factory managers often have forged alliances with local officials who are more interested in attracting investment and collecting bribes than taking steps that could slow the booming economy.

Ma Jun, author of a book about the pollution and mismanagement of China's water supplies, said it would be difficult for the leadership to break these alliances without systemic reforms allowing the public to play a greater role in governance.

"They can't count on self-discipline and they can't do it on their own," Ma said. "They need external forces. They need to use public pressure." For example, he said, citizens should be given the right to know what substances firms are releasing into the environment so they can challenge them to change.

The explosion that polluted the Songhua occurred at a plant operated by Jilin Petrochemical Co., a subsidiary of one of China's largest and most influential state oil firms, China National Petroleum Corp. At least two other major accidents have occurred at Jilin Petrochemical in recent years, and the firm has long been the subject of pollution complaints by residents downstream. But the government named it one of China's 21 environmentally friendly model companies in October.

It is unclear what kind of relationship Wang, a municipal official, had with Jilin Petrochemical, a provincial-level firm. Reports in state media indicated he was named deputy mayor only a few months ago after serving in another leadership post in Jilin, a city of 4.2 million people 600 miles northeast of Beijing. He was responsible for managing the city's industrial sector as well as departments in charge of traffic, social security, labor and work safety.

The morning after the explosion, Wang said at a news conference that the fire at the plant had been extinguished and that the blast would "not produce large-scale pollution."

"The air quality of the entire scene and surrounding areas meets standards. There are no toxic gases, and the water has not changed," he said, according to state media.

Wang's death came as the government announced it was setting up a team of high-level officials to investigate the cause of the explosion, the handling of the chemical spill and the damage done, and to discipline all those found responsible.

"Any coverup of the accident, and any negative attitude toward the probe, will be considered cheating the public and ignoring the authority of the government," said Li Yizhong, director of China's industrial safety agency, who was assigned to lead the team. His remarks, carried by the official New China News Agency, were the government's first explicit promise to address the coverup.

The head of Jilin Petrochemical, Yu Li, and two managers in the company have already been fired. Xie Zhenhua, director of the State Environmental Protection Administration, has also been dismissed. But it remains unclear when and what Xie was told about the spill, and whether he briefed any of China's senior leaders about it. Some have described him as a scapegoat, noting that he had been a strong environmental advocate during 12 years in the job.

"He's an outstanding official," said Wen Bo, the Beijing representative of the U.S.-based lobby group Pacific Environment. "He was a victim of the entire system. . . . They say they care about the environment, but when they allocate resources, they always prioritize economic development."