"Benzene-related chemicals, which were the main pollutants of the spill, remain at a safe level in the Songhua River," the China Daily newspaper quoted a State Environmental Protection Administration statement as saying.

The statement comes after reports of pollution in a Russian river fed by the Songhua, especially after the waterways began to thaw in spring.

Levels of cancer-causing chlorophenols were almost 30 times the allowable limits along sections of the Amur River in Russia's far east, Russian press reports quoted a local scientist as saying last month.

But China's environmental watchdog insisted that daily monitoring of the Songhua as well as the Heilong River, another affected waterway that also flows into the Amur, had revealed no excessive pollution.

"Water quality in the two rivers is steady and no pollution has occurred," according to the statement.

Around 100 tonnes of the carcinogens benzene and nitrobenzene poured into the 1,897-kilometer (1,172-mile) Songhua after an explosion in November at a chemical factory in northeast Jilin province.

Water supplies for millions of people living along the Songhua were suspended for days.

In Russia, there were fears that water and fish supplies for more than 600,000 people in the far eastern region of Khabarovsk had been contaminated.

China said on March 30 it would spend 1.2 billion dollars over five years to clean up the Songhua, although it indicated the project was due to long-term industrial pollution problems rather than the specific spill.

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China State Environmental Protection Administration