Environmental advocacy group Greenpeace said on Tuesday that an investigation it had conducted found tea bags sold in China by Unilever's Lipton brand contained unsafe levels of pesticide residue, though Unilever said the product was safe and to standard.

Greenpeace said in a statement that in March it randomly purchased several boxes of Lipton tea bags sold in two Beijing stores and sent them to an independent laboratory for pesticide residue testing.

"The testing found that all four Lipton samples contained pesticides that exceeded the EU's maximum levels of residue, while three samples contained pesticides unapproved by the EU," the group said.

"Some of the detected pesticides are also banned for use in tea production by the Chinese Ministry of Agriculture."

Greenpeace named one of the pesticides it found as the insecticide Bifenthrin, which is banned in the European Union.

Unilever said in a statement posted on its official Chinese microblogging account and confirmed by a company spokesman that all its Lipton tea products were safe.

"As a responsible multinational company, Unilever China has all along upheld high quality and the protection of consumers' rights. All the Lipton tea products we make are completely in line with national standards on pesticide residue, and are safe and up-to-standard goods," the company wrote.

Last November, China's quality watchdog said one of Unilever's Lipton tea varieties was found to contain unsafe levels of toxins. Unilever said that all those related tea products had been recalled and destroyed.

Lipton sells dozens of varieties of tea in China and is the dominant seller of tea bags in a country where consumers generally drink loose-leaf tea.

In recent months, several foreign firms have found themselves ensnared by Chinese product safety or quality probes, including U.S. retailer Wal-Mart Stores, McDonald's Corp and European retail giant Carrefour.

China has struggled to rein in health violations in the unruly and vast food sector despite harsh punishments and repeated vows to deal with the problem.

The country is notorious for its food safety woes, with regular news reports of fake cooking oil, tainted milk and even watermelons that explode from absorbing too much fertiliser.

However, both the American Chamber of Commerce in China and the European Union Chamber of Commerce in China have published reports saying foreign firms are sometimes unfairly singled out for punishment.